UploadVerification.php

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<?php
namespace MediaWiki\Upload;
 
use MediaWiki\Config\ConfigException;
use MediaWiki\Config\ServiceOptions;
use MediaWiki\MainConfigNames;
use MediaWiki\Media\MediaHandler;
use MediaWiki\Parser\Sanitizer;
use MediaWiki\Shell\Shell;
use Wikimedia\Mime\MimeAnalyzer;
use Wikimedia\Mime\XmlTypeCheck;
 
class UploadVerification {
 
    private const SAFE_XML_ENCODINGS = [
        'UTF-8',
        'US-ASCII',
        'ISO-8859-1',
        'ISO-8859-2',
        'UTF-16',
        'UTF-32',
        'WINDOWS-1250',
        'WINDOWS-1251',
        'WINDOWS-1252',
        'WINDOWS-1253',
        'WINDOWS-1254',
        'WINDOWS-1255',
        'WINDOWS-1256',
        'WINDOWS-1257',
        'WINDOWS-1258',
    ];
 
    public const CONSTRUCTOR_OPTIONS = [
        MainConfigNames::VerifyMimeType,
        MainConfigNames::MimeTypeExclusions,
        MainConfigNames::DisableUploadScriptChecks,
        MainConfigNames::Antivirus,
        MainConfigNames::AntivirusSetup,
        MainConfigNames::AntivirusRequired
    ];
 
    private ServiceOptions $config;
    private MimeAnalyzer $mimeAnalyzer;
    private SVGCSSChecker $SVGCSSChecker;
 
    public function __construct(
        ServiceOptions $config,
        MimeAnalyzer $mimeAnalyzer,
        SVGCSSChecker $SVGCSSChecker
    ) {
        $config->assertRequiredOptions( self::CONSTRUCTOR_OPTIONS );
        $this->config = $config;
        $this->mimeAnalyzer = $mimeAnalyzer;
        $this->SVGCSSChecker = $SVGCSSChecker;
    }
 
    private function verifyMimeType( $mime ) {
        $verifyMimeType = $this->config->get( MainConfigNames::VerifyMimeType );
        if ( $verifyMimeType ) {
            wfDebug( "mime: <$mime>" );
            $mimeTypeExclusions = $this->config
                ->get( MainConfigNames::MimeTypeExclusions );
            if ( UploadBase::checkFileExtension( $mime, $mimeTypeExclusions ) ) {
                return [ 'filetype-badmime', $mime ];
            }
        }
 
        return true;
    }
 
    public function verifyFile( string $path, string $ext, array $fileProps ) {
        $config = $this->config;
        $verifyMimeType = $config->get( MainConfigNames::VerifyMimeType );
        $disableUploadScriptChecks = $config->get( MainConfigNames::DisableUploadScriptChecks );
        $status = $this->verifyPartialFile( $path, $ext, $fileProps );
        if ( $status !== true ) {
            return $status;
        }
 
        $mime = $fileProps['mime'];
 
        if ( $verifyMimeType ) {
            # XXX: Missing extension will be caught by validateName() via getTitle()
            if ( $ext !== '' &&
                !$this->verifyExtension( $mime, $ext )
            ) {
                return [ 'filetype-mime-mismatch', $ext, $mime ];
            }
        }
 
        # check for htmlish code and javascript
        if ( !$disableUploadScriptChecks ) {
            if ( $ext === 'svg' || $mime === 'image/svg+xml' ) {
                $svgStatus = $this->detectScriptInSvg( $path, false );
                if ( $svgStatus !== false ) {
                    return $svgStatus;
                }
            }
        }
 
        $handler = $mime !== null ? MediaHandler::getHandler( $mime ) : null;
        if ( $handler ) {
            $handlerStatus = $handler->verifyUpload( $path );
            if ( !$handlerStatus->isOK() ) {
                $errors = $handlerStatus->getErrorsArray();
 
                return reset( $errors );
            }
        }
 
        // TODO: Perhaps we should have a hook here akin to UploadVerifyFile
        // except that it doesn't pass an UploadBase, and it would run
        // even when someone is verifying a file not going through UploadBase.
 
        wfDebug( __METHOD__ . ": all clear; passing." );
 
        return true;
    }
 
    public function verifyPartialFile( string $path, string $ext, array $fileProps ) {
        $config = $this->config;
        $disableUploadScriptChecks = $config->get( MainConfigNames::DisableUploadScriptChecks );
 
        # check MIME type, if desired
        $mime = $fileProps['file-mime'];
        $status = $this->verifyMimeType( $mime );
        if ( $status !== true ) {
            return $status;
        }
 
        # check for htmlish code and javascript
        if ( !$disableUploadScriptChecks ) {
            if ( $this->detectScript( $path, $mime, $ext ) ) {
                return [ 'uploadscripted' ];
            }
            if ( $ext === 'svg' || $mime === 'image/svg+xml' ) {
                $svgStatus = $this->detectScriptInSvg( $path, true );
                if ( $svgStatus !== false ) {
                    return $svgStatus;
                }
            }
        }
 
        # Scan the uploaded file for viruses
        $virus = $this->detectVirus( $path );
        if ( $virus ) {
            return [ 'uploadvirus', $virus ];
        }
 
        return true;
    }
 
    public function verifyExtension( $mime, $extension ) {
        $magic = $this->mimeAnalyzer;
 
        if ( !$mime || $mime === 'unknown' || $mime === 'unknown/unknown' ) {
            if ( !$magic->isRecognizableExtension( $extension ) ) {
                wfDebug( __METHOD__ . ": passing file with unknown detected mime type; " .
                    "unrecognized extension '$extension', can't verify" );
 
                return true;
            }
 
            wfDebug( __METHOD__ . ": rejecting file with unknown detected mime type; " .
                "recognized extension '$extension', so probably invalid file" );
            return false;
        }
 
        $match = $magic->isMatchingExtension( $extension, $mime );
 
        if ( $match === null ) {
            if ( $magic->getMimeTypesFromExtension( $extension ) !== [] ) {
                wfDebug( __METHOD__ . ": No extension known for $mime, but we know a mime for $extension" );
 
                return false;
            }
 
            wfDebug( __METHOD__ . ": no file extension known for mime type $mime, passing file" );
            return true;
        }
 
        if ( $match ) {
            wfDebug( __METHOD__ . ": mime type $mime matches extension $extension, passing file" );
 
            return true;
        }
 
        wfDebug( __METHOD__
            . ": mime type $mime mismatches file extension $extension, rejecting file" );
 
        return false;
    }
 
    public function detectScript( $file, $mime, $extension ) {
        # ugly hack: for text files, always look at the entire file.
        # For binary field, just check the first K.
 
        if ( str_starts_with( $mime ?? '', 'text/' ) ) {
            $chunk = file_get_contents( $file );
        } else {
            $fp = fopen( $file, 'rb' );
            if ( !$fp ) {
                return false;
            }
            $chunk = fread( $fp, 1024 );
            fclose( $fp );
        }
 
        $chunk = strtolower( $chunk );
 
        if ( !$chunk ) {
            return false;
        }
 
        # decode from UTF-16 if needed (could be used for obfuscation).
        if ( str_starts_with( $chunk, "\xfe\xff" ) ) {
            $enc = 'UTF-16BE';
        } elseif ( str_starts_with( $chunk, "\xff\xfe" ) ) {
            $enc = 'UTF-16LE';
        } else {
            $enc = null;
        }
 
        if ( $enc !== null ) {
            // phpcs:ignore Generic.PHP.NoSilencedErrors.Discouraged
            $chunk = @iconv( $enc, "ASCII//IGNORE", $chunk );
        }
 
        $chunk = trim( $chunk );
 
        wfDebug( __METHOD__ . ": checking for embedded scripts and HTML stuff" );
 
        # check for HTML doctype
        if ( preg_match( "/<!DOCTYPE *X?HTML/i", $chunk ) ) {
            return true;
        }
 
        // Some browsers will interpret obscure xml encodings as UTF-8, while
        // PHP/expat will interpret the given encoding in the xml declaration (T49304)
        if ( $extension === 'svg' || str_starts_with( $mime ?? '', 'image/svg' ) ) {
            if ( $this->checkXMLEncodingMismatch( $file ) ) {
                return true;
            }
        }
 
        // Quick check for HTML heuristics in old IE and Safari.
        //
        // The exact heuristics IE uses are checked separately via verifyMimeType(), so we
        // don't need them all here as it can cause many false positives.
        //
        // Check for `<script` and such still to forbid script tags and embedded HTML in SVG:
        $tags = [
            '<body',
            '<head',
            '<html', # also in safari
            '<script', # also in safari
        ];
 
        foreach ( $tags as $tag ) {
            if ( str_contains( $chunk, $tag ) ) {
                wfDebug( __METHOD__ . ": found something that may make it be mistaken for html: $tag" );
 
                return true;
            }
        }
 
        /*
         * look for JavaScript
         */
 
        # resolve entity-refs to look at attributes. may be harsh on big files... cache result?
        $chunk = Sanitizer::decodeCharReferences( $chunk );
 
        # look for script-types
        if ( preg_match( '!type\s*=\s*[\'"]?\s*(?:\w*/)?(?:ecma|java)!im', $chunk ) ) {
            wfDebug( __METHOD__ . ": found script types" );
 
            return true;
        }
 
        # look for html-style script-urls
        if ( preg_match( '!(?:href|src|data)\s*=\s*[\'"]?\s*(?:ecma|java)script:!im', $chunk ) ) {
            wfDebug( __METHOD__ . ": found html-style script urls" );
 
            return true;
        }
 
        # look for css-style script-urls
        if ( preg_match( '!url\s*\‍(\s*[\'"]?\s*(?:ecma|java)script:!im', $chunk ) ) {
            wfDebug( __METHOD__ . ": found css-style script urls" );
 
            return true;
        }
 
        wfDebug( __METHOD__ . ": no scripts found" );
 
        return false;
    }
 
    private function checkXMLEncodingMismatch( $file ) {
        // https://mimesniff.spec.whatwg.org/#resource-header says browsers
        // should read the first 1445 bytes. Do 4096 bytes for good measure.
        // XML Spec says XML declaration if present must be first thing in file
        // other than BOM
        $contents = file_get_contents( $file, false, null, 0, 4096 );
        $encodingRegex = '!encoding[ \t\n\r]*=[ \t\n\r]*[\'"](.*?)[\'"]!si';
 
        if ( preg_match( "!<\?xml\b(.*?)\?>!si", $contents, $matches ) ) {
            if ( preg_match( $encodingRegex, $matches[1], $encMatch )
                && !in_array( strtoupper( $encMatch[1] ), self::SAFE_XML_ENCODINGS )
            ) {
                wfDebug( __METHOD__ . ": Found unsafe XML encoding '{$encMatch[1]}'" );
 
                return true;
            }
        } elseif ( preg_match( "!<\?xml\b!i", $contents ) ) {
            // Start of XML declaration without an end in the first 4096 bytes
            // bytes. There shouldn't be a legitimate reason for this to happen.
            wfDebug( __METHOD__ . ": Unmatched XML declaration start" );
 
            return true;
        } elseif ( str_starts_with( $contents, "\x4C\x6F\xA7\x94" ) ) {
            // EBCDIC encoded XML
            wfDebug( __METHOD__ . ": EBCDIC Encoded XML" );
 
            return true;
        }
 
        // It's possible the file is encoded with multibyte encoding, so re-encode attempt to
        // detect the encoding in case it specifies an encoding not allowed in self::SAFE_XML_ENCODINGS
        $attemptEncodings = [ 'UTF-16', 'UTF-16BE', 'UTF-32', 'UTF-32BE' ];
        foreach ( $attemptEncodings as $encoding ) {
            // phpcs:ignore Generic.PHP.NoSilencedErrors.Discouraged
            $str = @iconv( $encoding, 'UTF-8', $contents );
            if ( $str != '' && preg_match( "!<\?xml\b(.*?)\?>!si", $str, $matches ) ) {
                if ( preg_match( $encodingRegex, $matches[1], $encMatch )
                    && !in_array( strtoupper( $encMatch[1] ), self::SAFE_XML_ENCODINGS )
                ) {
                    wfDebug( __METHOD__ . ": Found unsafe XML encoding '{$encMatch[1]}'" );
 
                    return true;
                }
            } elseif ( $str != '' && preg_match( "!<\?xml\b!i", $str ) ) {
                // Start of XML declaration without an end in the first 4096 bytes
                // bytes. There shouldn't be a legitimate reason for this to happen.
                wfDebug( __METHOD__ . ": Unmatched XML declaration start" );
 
                return true;
            }
        }
 
        return false;
    }
 
    private function detectScriptInSvg( $filename, $partial ) {
        $check = new XmlTypeCheck(
            $filename,
            $this->checkSvgScriptCallback( ... ),
            true,
            [
                'processing_instruction_handler' => $this->checkSvgPICallback( ... ),
                'external_dtd_handler' => $this->checkSvgExternalDTD( ... ),
            ]
        );
        if ( $check->wellFormed !== true ) {
            // Invalid xml (T60553)
            // But only when non-partial (T67724)
            return $partial ? false : [ 'uploadinvalidxml' ];
        }
 
        if ( $check->filterMatch ) {
            return $check->filterMatchType;
        }
 
        return false;
    }
 
    private function checkSvgPICallback( $target ) {
        // Don't allow external stylesheets (T59550)
        if ( preg_match( '/xml-stylesheet/i', $target ) ) {
            return [ 'upload-scripted-pi-callback' ];
        }
 
        return false;
    }
 
    private function checkSvgExternalDTD( $type, $publicId, $systemId ) {
        // This doesn't include the XHTML+MathML+SVG doctype since we don't
        // allow XHTML anyway.
        static $allowedDTDs = [
            'http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd',
            'http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd',
            'http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-basic.dtd',
            'http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-tiny.dtd',
            // https://phabricator.wikimedia.org/T168856
            'http://www.w3.org/TR/2001/PR-SVG-20010719/DTD/svg10.dtd',
        ];
        if ( $type !== 'PUBLIC'
            || !in_array( $systemId, $allowedDTDs )
            || !str_starts_with( $publicId, "-//W3C//" )
        ) {
            return [ 'upload-scripted-dtd' ];
        }
        return false;
    }
 
    private function checkSvgScriptCallback( $element, $attribs, $data = null ) {
        [ $namespace, $strippedElement ] = self::splitXmlNamespace( $element );
 
        // We specifically don't include:
        // http://www.w3.org/1999/xhtml (T62771)
        static $validNamespaces = [
            '',
            'adobe:ns:meta/',
            'http://cipa.jp/exif/1.0/',
            'http://creativecommons.org/ns#',
            'http://developer.sonyericsson.com/cell/1.0/',
            'http://inkscape.sourceforge.net/dtd/sodipodi-0.dtd',
            'http://iptc.org/std/iptc4xmpcore/1.0/xmlns/',
            'http://iptc.org/std/iptc4xmpext/2008-02-29/',
            'http://leica-camera.com/digital-shift-assistant/1.0/',
            'http://ns.acdsee.com/iptc/1.0/',
            'http://ns.acdsee.com/regions/',
            'http://ns.adobe.com/adobeillustrator/10.0/',
            'http://ns.adobe.com/adobesvgviewerextensions/3.0/',
            'http://ns.adobe.com/album/1.0/',
            'http://ns.adobe.com/camera-raw-defaults/1.0/',
            'http://ns.adobe.com/camera-raw-embedded-lens-profile/1.0/',
            'http://ns.adobe.com/camera-raw-saved-settings/1.0/',
            'http://ns.adobe.com/camera-raw-settings/1.0/',
            'http://ns.adobe.com/creatoratom/1.0/',
            'http://ns.adobe.com/dicom/',
            'http://ns.adobe.com/exif/1.0/',
            'http://ns.adobe.com/exif/1.0/aux/',
            'http://ns.adobe.com/extensibility/1.0/',
            'http://ns.adobe.com/flows/1.0/',
            'http://ns.adobe.com/hdr-gain-map/1.0/',
            'http://ns.adobe.com/hdr-metadata/1.0/',
            'http://ns.adobe.com/ix/1.0/',
            'http://ns.adobe.com/lightroom/1.0/',
            'http://ns.adobe.com/illustrator/1.0/',
            'http://ns.adobe.com/imagereplacement/1.0/',
            'http://ns.adobe.com/pdf/1.3/',
            'http://ns.adobe.com/pdfx/1.3/',
            'http://ns.adobe.com/photoshop/1.0/',
            'http://ns.adobe.com/photoshop/1.0/camera-profile',
            'http://ns.adobe.com/photoshop/1.0/panorama-profile',
            'http://ns.adobe.com/raw/1.0/',
            'http://ns.adobe.com/swf/1.0/',
            'http://ns.adobe.com/saveforweb/1.0/',
            'http://ns.adobe.com/tiff/1.0/',
            'http://ns.adobe.com/variables/1.0/',
            'http://ns.adobe.com/xap/1.0/',
            'http://ns.adobe.com/xap/1.0/bj/',
            'http://ns.adobe.com/xap/1.0/g/',
            'http://ns.adobe.com/xap/1.0/g/img/',
            'http://ns.adobe.com/xap/1.0/mm/',
            'http://ns.adobe.com/xap/1.0/plus/',
            'http://ns.adobe.com/xap/1.0/rights/',
            'http://ns.adobe.com/xap/1.0/stype/dimensions#',
            'http://ns.adobe.com/xap/1.0/stype/font#',
            'http://ns.adobe.com/xap/1.0/stype/manifestitem#',
            'http://ns.adobe.com/xap/1.0/stype/resourceevent#',
            'http://ns.adobe.com/xap/1.0/stype/resourceref#',
            'http://ns.adobe.com/xap/1.0/stype/version#',
            'http://ns.adobe.com/xap/1.0/t/pg/',
            'http://ns.adobe.com/xmp/1.0/dynamicmedia/',
            'http://ns.adobe.com/xmp/identifier/qual/1.0/',
            'http://ns.adobe.com/xmp/note/',
            'http://ns.adobe.com/xmp/stype/area#',
            'http://ns.apple.com/adjustment-settings/1.0/',
            'http://ns.apple.com/faceinfo/1.0/',
            'http://ns.apple.com/hdrgainmap/1.0/',
            'http://ns.apple.com/pixeldatainfo/1.0/',
            'http://ns.exiftool.org/1.0/',
            'http://ns.extensis.com/extensis/1.0/',
            'http://ns.fastpictureviewer.com/fpv/1.0/',
            'http://ns.google.com/photos/1.0/audio/',
            'http://ns.google.com/photos/1.0/camera/',
            'http://ns.google.com/photos/1.0/container/',
            'http://ns.google.com/photos/1.0/creations/',
            'http://ns.google.com/photos/1.0/depthmap/',
            'http://ns.google.com/photos/1.0/focus/',
            'http://ns.google.com/photos/1.0/image/',
            'http://ns.google.com/photos/1.0/panorama/',
            'http://ns.google.com/photos/dd/1.0/profile/',
            'http://ns.google.com/videos/1.0/spherical/',
            'http://ns.idimager.com/ics/1.0/',
            'http://ns.iview-multimedia.com/mediapro/1.0/',
            'http://ns.leiainc.com/photos/1.0/image/',
            'http://ns.microsoft.com/expressionmedia/1.0/',
            'http://ns.microsoft.com/photo/1.0',
            'http://ns.microsoft.com/photo/1.1',
            'http://ns.microsoft.com/photo/1.2/',
            'http://ns.microsoft.com/photo/1.2/t/region#',
            'http://ns.microsoft.com/photo/1.2/t/regioninfo#',
            'http://ns.nikon.com/asteroid/1.0/',
            'http://ns.nikon.com/nine/1.0/',
            'http://ns.nikon.com/sdc/1.0/',
            'http://ns.optimasc.com/dex/1.0/',
            'http://ns.seal/2024/1.0/',
            'http://ns.useplus.org/ldf/xmp/1.0/',
            'http://prismstandard.org/namespaces/basic/2.0/',
            'http://prismstandard.org/namespaces/pmi/2.2/',
            'http://prismstandard.org/namespaces/prismusagerights/2.1/',
            'http://prismstandard.org/namespaces/prl/2.1/',
            'http://prismstandard.org/namespaces/prm/3.0/',
            'http://purl.org/dc/elements/1.1/',
            'http://purl.org/dc/elements/1.1',
            'http://rs.tdwg.org/dwc/index.htm',
            'http://schemas.microsoft.com/visio/2003/svgextensions/',
            'http://sodipodi.sourceforge.net/dtd/sodipodi-0.dtd',
            'http://taptrix.com/inkpad/svg_extensions',
            'http://www.digikam.org/ns/1.0/',
            'http://www.dji.com/drone-dji/1.0/',
            'http://www.metadataworkinggroup.com/schemas/collections/',
            'http://www.metadataworkinggroup.com/schemas/keywords/',
            'http://www.metadataworkinggroup.com/schemas/regions/',
            'http://web.resource.org/cc/',
            'http://www.freesoftware.fsf.org/bkchem/cdml',
            'http://www.inkscape.org/namespaces/inkscape',
            'http://www.opengis.net/gml',
            'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
            'http://www.w3.org/2000/01/rdf-schema#',
            'http://www.w3.org/2000/svg',
            'http://www.w3.org/2000/02/svg/testsuite/description/', // T278044
            'http://www.w3.org/tr/rec-rdf-syntax/',
            'http://xmp.gettyimages.com/gift/1.0/',
        ];
 
        // Inkscape mangles namespace definitions created by Adobe Illustrator.
        // This is nasty but harmless. (T144827)
        $isBuggyInkscape = preg_match( '/^&(#38;)*ns_[a-z_]+;$/', $namespace );
 
        if ( !( $isBuggyInkscape || in_array( $namespace, $validNamespaces ) ) ) {
            wfDebug( __METHOD__ . ": Non-svg namespace '$namespace' in uploaded file." );
            return [ 'uploadscriptednamespace', $namespace ];
        }
 
        // check for elements that can contain javascript
        if ( $strippedElement === 'script' ) {
            wfDebug( __METHOD__ . ": Found script element '$element' in uploaded file." );
 
            return [ 'uploaded-script-svg', $strippedElement ];
        }
 
        // e.g., <svg xmlns="http://www.w3.org/2000/svg">
        //  <handler xmlns:ev="http://www.w3.org/2001/xml-events" ev:event="load">alert(1)</handler> </svg>
        if ( $strippedElement === 'handler' ) {
            wfDebug( __METHOD__ . ": Found scriptable element '$element' in uploaded file." );
 
            return [ 'uploaded-script-svg', $strippedElement ];
        }
 
        // SVG reported in Feb '12 that used xml:stylesheet to generate javascript block
        if ( $strippedElement === 'stylesheet' ) {
            wfDebug( __METHOD__ . ": Found scriptable element '$element' in uploaded file." );
 
            return [ 'uploaded-script-svg', $strippedElement ];
        }
 
        // Block iframes, in case they pass the namespace check
        if ( $strippedElement === 'iframe' ) {
            wfDebug( __METHOD__ . ": iframe in uploaded file." );
 
            return [ 'uploaded-script-svg', $strippedElement ];
        }
 
        // Check <style> css
        if ( $strippedElement === 'style' ) {
            $cssCheck = $this->SVGCSSChecker->checkStyleTag( $data );
            if ( $cssCheck !== true ) {
                wfDebug( __METHOD__ . ": hostile css in style element. " . $cssCheck[0] );
 
                return [ 'uploaded-hostile-svg', $cssCheck[0], $cssCheck[1], $cssCheck[2] ];
            }
        }
 
        static $cssAttrs = [ 'font', 'clip-path', 'fill', 'filter', 'marker',
            'marker-end', 'marker-mid', 'marker-start', 'mask', 'stroke', 'cursor' ];
 
        foreach ( $attribs as $attrib => $value ) {
            // If attributeNamespace is '', it is relative to its element's namespace
            [ $attributeNamespace, $stripped ] = self::splitXmlNamespace( $attrib );
            $value = strtolower( $value );
 
            if ( !(
                    // Inkscape element's have valid attribs that start with on and are safe, fail all others
                    // We are assuming here that the SVG will be interpreted
                    // under XML serialization. This is not safe for SVGs
                    // embedded directly in HTML.
                    $namespace === 'http://www.inkscape.org/namespaces/inkscape' &&
                    $attributeNamespace === ''
                ) && str_starts_with( $stripped, 'on' )
            ) {
                wfDebug( __METHOD__
                    . ": Found event-handler attribute '$attrib'='$value' in uploaded file." );
 
                return [ 'uploaded-event-handler-on-svg', $attrib, $value ];
            }
 
            // Do not allow relative links, or unsafe url schemas.
            // For <a> tags, only data:, http: and https: and same-document
            // fragment links are allowed.
            // For all other tags, only 'data:' and fragments (#) are allowed.
            if (
                $stripped === 'href'
                && $value !== ''
                && !str_starts_with( $value, 'data:' )
                && !str_starts_with( $value, '#' )
                && !( $strippedElement === 'a' && preg_match( '!^https?://!i', $value ) )
            ) {
                wfDebug( __METHOD__ . ": Found href attribute <$strippedElement "
                    . "'$attrib'='$value' in uploaded file." );
 
                return [ 'uploaded-href-attribute-svg', $strippedElement, $attrib, $value ];
            }
 
            // Only allow 'data:\' targets that should be safe.
            // This prevents vectors like image/svg, text/xml, application/xml, and text/html, which can contain scripts
            if ( $stripped === 'href' && strncasecmp( 'data:', $value, 5 ) === 0 ) {
                // RFC2397 parameters.
                // This is only slightly slower than (;[\w;]+)*.
                // phpcs:ignore Generic.Files.LineLength
                $parameters = '(?>;[a-zA-Z0-9\!#$&\'*+.^_`{|}~-]+=(?>[a-zA-Z0-9\!#$&\'*+.^_`{|}~-]+|"(?>[\0-\x0c\x0e-\x21\x23-\x5b\x5d-\x7f]+|\\\\[\0-\x7f])*"))*(?:;base64)?';
 
                if ( !preg_match( "!^data:\s*image/(gif|jpeg|jpg|a?png|webp|avif)$parameters,!i", $value ) ) {
                    wfDebug( __METHOD__ . ": Found href with data URI with MIME type that is not allowed "
                        . "\"<$strippedElement '$attrib'='$value'...\" in uploaded file." );
                    return [ 'uploaded-href-unsafe-target-svg', $strippedElement, $attrib, $value ];
                }
            }
 
            // Change href with animate from (http://html5sec.org/#137).
            if ( $stripped === 'attributename'
                && $strippedElement === 'animate'
                && $this->stripXmlNamespace( $value ) === 'href'
            ) {
                wfDebug( __METHOD__ . ": Found animate that might be changing href using from "
                    . "\"<$strippedElement '$attrib'='$value'...\" in uploaded file." );
 
                return [ 'uploaded-animate-svg', $strippedElement, $attrib, $value ];
            }
 
            // Use set/animate to add event-handler attribute to parent.
            if ( ( $strippedElement === 'set' || $strippedElement === 'animate' )
                && $stripped === 'attributename'
                && str_starts_with( $value, 'on' )
            ) {
                wfDebug( __METHOD__ . ": Found svg setting event-handler attribute with "
                    . "\"<$strippedElement $stripped='$value'...\" in uploaded file." );
 
                return [ 'uploaded-setting-event-handler-svg', $strippedElement, $stripped, $value ];
            }
 
            // use set to add href attribute to parent element.
            if ( $strippedElement === 'set'
                && $stripped === 'attributename'
                && str_contains( $value, 'href' )
            ) {
                wfDebug( __METHOD__ . ": Found svg setting href attribute '$value' in uploaded file." );
 
                return [ 'uploaded-setting-href-svg' ];
            }
 
            // use set to add a remote / data / script target to an element.
            if ( $strippedElement === 'set'
                && $stripped === 'to'
                && preg_match( '!(http|https|data|script):!im', $value )
            ) {
                wfDebug( __METHOD__ . ": Found svg setting attribute to '$value' in uploaded file." );
 
                return [ 'uploaded-wrong-setting-svg', $value ];
            }
 
            // use handler attribute with remote / data / script.
            if ( $stripped === 'handler' && preg_match( '!(http|https|data|script):!im', $value ) ) {
                wfDebug( __METHOD__ . ": Found svg setting handler with remote/data/script "
                    . "'$attrib'='$value' in uploaded file." );
 
                return [ 'uploaded-setting-handler-svg', $attrib, $value ];
            }
 
            // use CSS styles to bring in remote code.
            if ( $stripped === 'style'
                && $this->SVGCSSChecker->checkStyleAttribute( $value ) !== true
            ) {
                wfDebug( __METHOD__ . ": Found svg setting a style with "
                    . "remote url '$attrib'='$value' in uploaded file." );
                return [ 'uploaded-remote-url-svg', $attrib, $value ];
            }
 
            // Several attributes can include css, css character escaping isn't allowed.
            if ( in_array( $stripped, $cssAttrs, true )
                && $this->SVGCSSChecker->checkPresentationalAttribute( $value ) !== true
            ) {
                wfDebug( __METHOD__ . ": Found svg setting a style with "
                    . "remote url '$attrib'='$value' in uploaded file." );
                return [ 'uploaded-remote-url-svg', $attrib, $value ];
            }
 
            // image filters can pull in url, which could be svg that executes scripts.
            // Only allow url( "#foo" ).
            // Do not allow url( http://example.com )
            // TODO: It seems like the line above already does this check.
            if ( $strippedElement === 'image'
                && $stripped === 'filter'
                && preg_match( '!url\s*\‍(\s*["\']?[^#]!im', $value )
            ) {
                wfDebug( __METHOD__ . ": Found image filter with url: "
                    . "\"<$strippedElement $stripped='$value'...\" in uploaded file." );
 
                return [ 'uploaded-image-filter-svg', $strippedElement, $stripped, $value ];
            }
        }
 
        return false; // No scripts detected
    }
 
    private function splitXmlNamespace( $element ) {
        // 'http://www.w3.org/2000/svg:script' -> [ 'http://www.w3.org/2000/svg', 'script' ]
        $parts = explode( ':', strtolower( $element ) );
        $name = array_pop( $parts );
        $ns = implode( ':', $parts );
 
        return [ $ns, $name ];
    }
 
    private function stripXmlNamespace( $element ) {
        // 'http://www.w3.org/2000/svg:script' -> 'script'
        return self::splitXmlNamespace( $element )[1];
    }
 
    public function detectVirus( $file ) {
        $mainConfig = $this->config;
        $antivirus = $mainConfig->get( MainConfigNames::Antivirus );
        $antivirusSetup = $mainConfig->get( MainConfigNames::AntivirusSetup );
        $antivirusRequired = $mainConfig->get( MainConfigNames::AntivirusRequired );
        if ( !$antivirus ) {
            wfDebug( __METHOD__ . ": virus scanner disabled" );
 
            return null;
        }
 
        if ( !( $antivirusSetup[$antivirus] ?? false ) ) {
            throw new ConfigException( "Unknown virus scanner: $antivirus" );
        }
 
        # look up scanner configuration
        $command = $antivirusSetup[$antivirus]['command'];
        $exitCodeMap = $antivirusSetup[$antivirus]['codemap'];
        $msgPattern = $antivirusSetup[$antivirus]['messagepattern'] ?? null;
 
        if ( !str_contains( $command, "%f" ) ) {
            # simple pattern: append file to scan
            $command .= " " . Shell::escape( $file );
        } else {
            # complex pattern: replace "%f" with file to scan
            $command = str_replace( "%f", Shell::escape( $file ), $command );
        }
 
        wfDebug( __METHOD__ . ": running virus scan: $command " );
 
        # execute virus scanner
        $exitCode = false;
 
        # NOTE: there's a 50-line workaround to make stderr redirection work on windows, too.
        #  that does not seem to be worth the pain.
        #  Ask me (Duesentrieb) about it if it's ever needed.
        $output = wfShellExecWithStderr( $command, $exitCode );
 
        # map exit code to AV_xxx constants.
        $mappedCode = $exitCode;
        if ( $exitCodeMap ) {
            if ( isset( $exitCodeMap[$exitCode] ) ) {
                $mappedCode = $exitCodeMap[$exitCode];
            } elseif ( isset( $exitCodeMap["*"] ) ) {
                $mappedCode = $exitCodeMap["*"];
            }
        }
 
        # NB: AV_NO_VIRUS is 0, but AV_SCAN_FAILED is false,
        # so we need the strict equalities === and thus can't use a switch here
        if ( $mappedCode === AV_SCAN_FAILED ) {
            # scan failed (code was mapped to false by $exitCodeMap)
            wfDebug( __METHOD__ . ": failed to scan $file (code $exitCode)." );
 
            $output = $antivirusRequired
                ? wfMessage( 'virus-scanfailed', [ $exitCode ] )->text()
                : null;
        } elseif ( $mappedCode === AV_SCAN_ABORTED ) {
            # scan failed because filetype is unknown (probably immune)
            wfDebug( __METHOD__ . ": unsupported file type $file (code $exitCode)." );
            $output = null;
        } elseif ( $mappedCode === AV_NO_VIRUS ) {
            # no virus found
            wfDebug( __METHOD__ . ": file passed virus scan." );
            $output = false;
        } else {
            $output = trim( $output );
 
            if ( !$output ) {
                $output = true; # if there's no output, return true
            } elseif ( $msgPattern ) {
                $groups = [];
                if ( preg_match( $msgPattern, $output, $groups ) && $groups[1] ) {
                    $output = $groups[1];
                }
            }
 
            wfDebug( __METHOD__ . ": FOUND VIRUS! scanner feedback: $output" );
        }
 
        return $output;
    }
}