ContentSecurityPolicy.php

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<?php
use MediaWiki\HookContainer\HookContainer;
use MediaWiki\HookContainer\HookRunner;
use MediaWiki\MediaWikiServices;
 
class ContentSecurityPolicy {
    public const REPORT_ONLY_MODE = 1;
    public const FULL_MODE = 2;
 
    private $nonce;
    private $mwConfig;
    private $response;
 
    private $extraDefaultSrc = [];
    private $extraScriptSrc = [];
    private $extraStyleSrc = [];
 
    private $hookRunner;
 
    public function __construct( WebResponse $response, Config $mwConfig,
        HookContainer $hookContainer
    ) {
        $this->response = $response;
        $this->mwConfig = $mwConfig;
        $this->hookRunner = new HookRunner( $hookContainer );
    }
 
    public function sendCSPHeader( $csp, $reportOnly ) {
        $policy = $this->makeCSPDirectives( $csp, $reportOnly );
        $headerName = $this->getHeaderName( $reportOnly );
        if ( $policy ) {
            $this->response->header(
                "$headerName: $policy"
            );
        }
    }
 
    public function sendHeaders() {
        $cspConfig = $this->mwConfig->get( 'CSPHeader' );
        $cspConfigReportOnly = $this->mwConfig->get( 'CSPReportOnlyHeader' );
 
        $this->sendCSPHeader( $cspConfig, self::FULL_MODE );
        $this->sendCSPHeader( $cspConfigReportOnly, self::REPORT_ONLY_MODE );
 
        // This used to insert a <meta> tag here, per advice at
        // https://blogs.dropbox.com/tech/2015/09/unsafe-inline-and-nonce-deployment/
        // The goal was to prevent nonce from working after the page hit onready,
        // This would help in old browsers that didn't support nonces, and
        // also assist for varnish-cached pages which repeat nonces.
        // However, this is incompatible with how resource loader storage works
        // via mw.domEval() so it was removed.
    }
 
    private function getHeaderName( $reportOnly ) {
        if ( $reportOnly === self::REPORT_ONLY_MODE ) {
            return 'Content-Security-Policy-Report-Only';
        }
 
        if ( $reportOnly === self::FULL_MODE ) {
            return 'Content-Security-Policy';
        }
        throw new UnexpectedValueException( "Mode '$reportOnly' not recognised" );
    }
 
    private function makeCSPDirectives( $policyConfig, $mode ) {
        if ( $policyConfig === false ) {
            // CSP is disabled
            return '';
        }
        if ( $policyConfig === true ) {
            $policyConfig = [];
        }
 
        $mwConfig = $this->mwConfig;
 
        if (
            !self::isNonceRequired( $mwConfig ) &&
            self::isNonceRequiredArray( [ $policyConfig ] )
        ) {
            // If the current policy requires a nonce, but the global state
            // does not, that's bad. Throw an exception. This should never happen.
            throw new LogicException( "Nonce requirement mismatch" );
        }
 
        $additionalSelfUrls = $this->getAdditionalSelfUrls();
        $additionalSelfUrlsScript = $this->getAdditionalSelfUrlsScript();
 
        // If no default-src is sent at all, it
        // seems browsers (or at least some), interpret
        // that as allow anything, but the spec seems
        // to imply that data: and blob: should be
        // blocked.
        $defaultSrc = [ '*', 'data:', 'blob:' ];
 
        $imgSrc = false;
        $scriptSrc = [ "'unsafe-eval'", "blob:", "'self'" ];
        if ( $policyConfig['useNonces'] ?? true ) {
            $scriptSrc[] = "'nonce-" . $this->getNonce() . "'";
        }
 
        $scriptSrc = array_merge( $scriptSrc, $additionalSelfUrlsScript );
        if ( isset( $policyConfig['script-src'] )
            && is_array( $policyConfig['script-src'] )
        ) {
            foreach ( $policyConfig['script-src'] as $src ) {
                $scriptSrc[] = $this->escapeUrlForCSP( $src );
            }
        }
        // Note: default on if unspecified.
        if ( $policyConfig['unsafeFallback'] ?? true ) {
            // unsafe-inline should be ignored on browsers
            // that support 'nonce-foo' sources.
            // Some older versions of firefox don't follow this
            // rule, but new browsers do. (Should be for at least
            // firefox 40+).
            $scriptSrc[] = "'unsafe-inline'";
        }
        // If default source option set to true or
        // an array of urls, set a restrictive default-src.
        // If set to false, we send a lenient default-src,
        // see the code above where $defaultSrc is set initially.
        if ( isset( $policyConfig['default-src'] )
            && $policyConfig['default-src'] !== false
        ) {
            $defaultSrc = array_merge(
                [ "'self'", 'data:', 'blob:' ],
                $additionalSelfUrls
            );
            if ( is_array( $policyConfig['default-src'] ) ) {
                foreach ( $policyConfig['default-src'] as $src ) {
                    $defaultSrc[] = $this->escapeUrlForCSP( $src );
                }
            }
        }
 
        if ( $policyConfig['includeCORS'] ?? true ) {
            $CORSUrls = $this->getCORSSources();
            if ( !in_array( '*', $defaultSrc ) ) {
                $defaultSrc = array_merge( $defaultSrc, $CORSUrls );
            }
            // Unlikely to have * in scriptSrc, but doesn't
            // hurt to check.
            if ( !in_array( '*', $scriptSrc ) ) {
                $scriptSrc = array_merge( $scriptSrc, $CORSUrls );
            }
        }
 
        $defaultSrc = array_merge( $defaultSrc, $this->extraDefaultSrc );
        $scriptSrc = array_merge( $scriptSrc, $this->extraScriptSrc );
 
        $cssSrc = array_merge( $defaultSrc, $this->extraStyleSrc, [ "'unsafe-inline'" ] );
 
        $this->hookRunner->onContentSecurityPolicyDefaultSource( $defaultSrc, $policyConfig, $mode );
        $this->hookRunner->onContentSecurityPolicyScriptSource( $scriptSrc, $policyConfig, $mode );
 
        if ( isset( $policyConfig['report-uri'] ) && $policyConfig['report-uri'] !== true ) {
            if ( $policyConfig['report-uri'] === false ) {
                $reportUri = false;
            } else {
                $reportUri = $this->escapeUrlForCSP( $policyConfig['report-uri'] );
            }
        } else {
            $reportUri = $this->getReportUri( $mode );
        }
 
        // Only send an img-src, if we're sending a restricitve default.
        if ( !is_array( $defaultSrc )
            || !in_array( '*', $defaultSrc )
            || !in_array( 'data:', $defaultSrc )
            || !in_array( 'blob:', $defaultSrc )
        ) {
            // A future todo might be to make the whitelist options only
            // add all the whitelisted sites to the header, instead of
            // allowing all (Assuming there is a small number of sites).
            // For now, the external image feature disables the limits
            // CSP puts on external images.
            if ( $mwConfig->get( 'AllowExternalImages' )
                || $mwConfig->get( 'AllowExternalImagesFrom' )
                || $mwConfig->get( 'AllowImageTag' )
            ) {
                $imgSrc = [ '*', 'data:', 'blob:' ];
            } elseif ( $mwConfig->get( 'EnableImageWhitelist' ) ) {
                $whitelist = wfMessage( 'external_image_whitelist' )
                    ->inContentLanguage()
                    ->plain();
                if ( preg_match( '/^\s*[^\s#]/m', $whitelist ) ) {
                    $imgSrc = [ '*', 'data:', 'blob:' ];
                }
            }
        }
        // Default value 'none'. true is none, false is nothing, string is single directive,
        // array is list.
        if ( !isset( $policyConfig['object-src'] ) || $policyConfig['object-src'] === true ) {
            $objectSrc = [ "'none'" ];
        } else {
            $objectSrc = (array)( $policyConfig['object-src'] ?: [] );
        }
        $objectSrc = array_map( [ $this, 'escapeUrlForCSP' ], $objectSrc );
 
        $directives = [];
        if ( $scriptSrc ) {
            $directives[] = 'script-src ' . implode( ' ', array_unique( $scriptSrc ) );
        }
        if ( $defaultSrc ) {
            $directives[] = 'default-src ' . implode( ' ', array_unique( $defaultSrc ) );
        }
        if ( $cssSrc ) {
            $directives[] = 'style-src ' . implode( ' ', array_unique( $cssSrc ) );
        }
        if ( $imgSrc ) {
            $directives[] = 'img-src ' . implode( ' ', array_unique( $imgSrc ) );
        }
        if ( $objectSrc ) {
            $directives[] = 'object-src ' . implode( ' ', $objectSrc );
        }
        if ( $reportUri ) {
            $directives[] = 'report-uri ' . $reportUri;
        }
 
        $this->hookRunner->onContentSecurityPolicyDirectives( $directives, $policyConfig, $mode );
 
        return implode( '; ', $directives );
    }
 
    private function getReportUri( $mode ) {
        $apiArguments = [
            'action' => 'cspreport',
            'format' => 'json'
        ];
        if ( $mode === self::REPORT_ONLY_MODE ) {
            $apiArguments['reportonly'] = '1';
        }
        $reportUri = wfAppendQuery( wfScript( 'api' ), $apiArguments );
 
        // Per spec, ';' and ',' must be hex-escaped in report URI
        $reportUri = $this->escapeUrlForCSP( $reportUri );
        return $reportUri;
    }
 
    private function prepareUrlForCSP( $url ) {
        $result = false;
        if ( preg_match( '/^[a-z][a-z0-9+.-]*:$/i', $url ) ) {
            // A schema source (e.g. blob: or data:)
            return $url;
        }
        $bits = wfParseUrl( $url );
        if ( !$bits && strpos( $url, '/' ) === false ) {
            // probably something like example.com.
            // try again protocol-relative.
            $url = '//' . $url;
            $bits = wfParseUrl( $url );
        }
        if ( $bits && isset( $bits['host'] )
            && $bits['host'] !== $this->mwConfig->get( 'ServerName' )
        ) {
            $result = $bits['host'];
            if ( $bits['scheme'] !== '' ) {
                $result = $bits['scheme'] . $bits['delimiter'] . $result;
            }
            if ( isset( $bits['port'] ) ) {
                $result .= ':' . $bits['port'];
            }
            $result = $this->escapeUrlForCSP( $result );
        }
        return $result;
    }
 
    private function getAdditionalSelfUrlsScript() {
        $additionalUrls = [];
        // wgExtensionAssetsPath for ?debug=true mode
        $pathVars = [ 'LoadScript', 'ExtensionAssetsPath', 'ResourceBasePath' ];
 
        foreach ( $pathVars as $path ) {
            $url = $this->mwConfig->get( $path );
            $preparedUrl = $this->prepareUrlForCSP( $url );
            if ( $preparedUrl ) {
                $additionalUrls[] = $preparedUrl;
            }
        }
        $RLSources = $this->mwConfig->get( 'ResourceLoaderSources' );
        foreach ( $RLSources as $wiki => $sources ) {
            foreach ( $sources as $id => $value ) {
                $url = $this->prepareUrlForCSP( $value );
                if ( $url ) {
                    $additionalUrls[] = $url;
                }
            }
        }
 
        return array_unique( $additionalUrls );
    }
 
    private function getAdditionalSelfUrls() {
        // XXX on a foreign repo, the included description page can have anything on it,
        // including inline scripts. But nobody sane does that.
 
        // In principle, you can have even more complex configs... (e.g. The urlsByExt option)
        $pathUrls = [];
        $additionalSelfUrls = [];
 
        // Future todo: The zone urls should never go into
        // style-src. They should either be only in img-src, or if
        // img-src unspecified they should be in default-src. Similarly,
        // the DescriptionStylesheetUrl only needs to be in style-src
        // (or default-src if style-src unspecified).
        $callback = function ( $repo, &$urls ) {
            $urls[] = $repo->getZoneUrl( 'public' );
            $urls[] = $repo->getZoneUrl( 'transcoded' );
            $urls[] = $repo->getZoneUrl( 'thumb' );
            $urls[] = $repo->getDescriptionStylesheetUrl();
        };
        $repoGroup = MediaWikiServices::getInstance()->getRepoGroup();
        $localRepo = $repoGroup->getRepo( 'local' );
        $callback( $localRepo, $pathUrls );
        $repoGroup->forEachForeignRepo( $callback, [ &$pathUrls ] );
 
        // Globals that might point to a different domain
        $pathGlobals = [ 'LoadScript', 'ExtensionAssetsPath', 'StylePath', 'ResourceBasePath' ];
        foreach ( $pathGlobals as $path ) {
            $pathUrls[] = $this->mwConfig->get( $path );
        }
        foreach ( $pathUrls as $path ) {
            $preparedUrl = $this->prepareUrlForCSP( $path );
            if ( $preparedUrl !== false ) {
                $additionalSelfUrls[] = $preparedUrl;
            }
        }
        $RLSources = $this->mwConfig->get( 'ResourceLoaderSources' );
 
        foreach ( $RLSources as $wiki => $sources ) {
            foreach ( $sources as $id => $value ) {
                $url = $this->prepareUrlForCSP( $value );
                if ( $url ) {
                    $additionalSelfUrls[] = $url;
                }
            }
        }
 
        return array_unique( $additionalSelfUrls );
    }
 
    private function getCORSSources() {
        $additionalUrls = [];
        $CORSSources = $this->mwConfig->get( 'CrossSiteAJAXdomains' );
        foreach ( $CORSSources as $source ) {
            if ( strpos( $source, '?' ) !== false ) {
                // CSP doesn't support single char wildcard
                continue;
            }
            $url = $this->prepareUrlForCSP( $source );
            if ( $url ) {
                $additionalUrls[] = $url;
            }
        }
        return $additionalUrls;
    }
 
    private function escapeUrlForCSP( $url ) {
        return str_replace(
            [ ';', ',' ],
            [ '%3B', '%2C' ],
            $url
        );
    }
 
    public static function falsePositiveBrowser( $ua ) {
        return (bool)preg_match( '!Firefox/4[0-2]\.!', $ua );
    }
 
    public static function isNonceRequired( Config $config ) {
        $configs = [
            $config->get( 'CSPHeader' ),
            $config->get( 'CSPReportOnlyHeader' )
        ];
        return self::isNonceRequiredArray( $configs );
    }
 
    private static function isNonceRequiredArray( array $configs ) {
        foreach ( $configs as $headerConfig ) {
            if (
                $headerConfig === true ||
                ( is_array( $headerConfig ) &&
                !isset( $headerConfig['useNonces'] ) ) ||
                ( is_array( $headerConfig ) &&
                isset( $headerConfig['useNonces'] ) &&
                $headerConfig['useNonces'] )
            ) {
                return true;
            }
        }
        return false;
    }
 
    public function getNonce() {
        if ( !self::isNonceRequired( $this->mwConfig ) ) {
            return false;
        }
        if ( $this->nonce === null ) {
            $rand = random_bytes( 15 );
            $this->nonce = base64_encode( $rand );
        }
 
        return $this->nonce;
    }
 
    public function addDefaultSrc( $source ) {
        $this->extraDefaultSrc[] = $this->prepareUrlForCSP( $source );
    }
 
    public function addStyleSrc( $source ) {
        $this->extraStyleSrc[] = $this->prepareUrlForCSP( $source );
    }
 
    public function addScriptSrc( $source ) {
        $this->extraScriptSrc[] = $this->prepareUrlForCSP( $source );
    }
}