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GHSA-h5vq-qfcg-4m6pmedium6.9

Symfony's HtmlSanitizer URL Attributes Pass Through BiDi Override Characters → Visual href Spoofing

Impact

Symfony\Component\HtmlSanitizer\TextSanitizer\UrlSanitizer::parse() (used by UrlSanitizer::sanitize() and therefore by every HtmlSanitizer config that allows links or media) accepts URLs that contain Unicode explicit-direction BiDi formatting characters: U+202A–U+202E (LRE / RLE / PDF / LRO / RLO) and U+2066–U+2069 (LRI / RLI / FSI / PDI). These characters are passed through unchanged into the href / src attributes produced by HtmlSanitizer. When the resulting HTML is rendered in a browser, the override characters reverse or alter the visual ordering of the URL text, so the displayed link…

Source excerpt · OSV

Affected packages

Start with the recorded fix for your release branch. Check your installed version and test compatibility before upgrading. Fixing this advisory does not rule out other vulnerabilities in the release.

symfony/html-sanitizer Packagist
Affected rangeRecorded fix
From 6.1.0 before 6.4.40Ecosystem versions6.4.40
From 7.0.0 before 7.4.12Ecosystem versions7.4.12
From 8.0.0 before 8.0.12Ecosystem versions8.0.12

Version evidence: OSV · GHSA-h5vq-qfcg-4m6p

View original version evidence (67 explicit versions)
symfony/symfony Packagist
Affected rangeRecorded fix
From 6.1.0 before 6.4.40Ecosystem versions6.4.40
From 7.0.0 before 7.4.12Ecosystem versions7.4.12
From 8.0.0 before 8.0.12Ecosystem versions8.0.12

Version evidence: OSV · GHSA-h5vq-qfcg-4m6p

View original version evidence (178 explicit versions)

Original source description

Description

Symfony\Component\HtmlSanitizer\TextSanitizer\UrlSanitizer::parse() (used by UrlSanitizer::sanitize() and therefore by every HtmlSanitizer config that allows links or media) accepts URLs that contain Unicode explicit-direction BiDi formatting characters: U+202A–U+202E (LRE / RLE / PDF / LRO / RLO) and U+2066–U+2069 (LRI / RLI / FSI / PDI). These characters are passed through unchanged into the href / src attributes produced by HtmlSanitizer. When the resulting HTML is rendered in a browser, the override characters reverse or alter the visual ordering of the URL text, so the displayed link can differ arbitrarily from the actual destination: a classic visual-spoofing / phishing primitive against viewers of sanitized content.

Resolution

UrlSanitizer::parse() now rejects URLs containing the explicit-direction BiDi formatting code points (U+202A–U+202E, U+2066–U+2069) before invoking the underlying URL parser. As an unrelated companion fix in the same patch, spaces inside path/query/fragment are now percent-encoded rather than rejected outright, while spaces in the scheme/authority remain rejected by the post-encoding whitespace check.

The patch for this issue is available here for branch 5.4.

Credits

Symfony would like to thank Himanshu Anand for reporting the issue and Nicolas Grekas for providing the fix.

References