GHSA-h5vq-qfcg-4m6p
Fix: symfony/symfony@743a435GHSA-h5vq-qfcg-4m6p is a CWE-451 vulnerability in symfony/html-sanitizer. O3 Security confirms whether GHSA-h5vq-qfcg-4m6p is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Symfony's HtmlSanitizer URL Attributes Pass Through BiDi Override Characters → Visual href Spoofing
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-h5vq-qfcg-4m6p.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
symfony/html-sanitizer🐘symfony/html-sanitizer🐘symfony/html-sanitizer🐘symfony/symfony🐘symfony/symfony🐘symfony/symfonyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | symfony/html-sanitizer | ≥ 6.1.0&&< 6.4.40 | 6.4.40 |
| 🐘Packagist | symfony/html-sanitizer | ≥ 7.0.0&&< 7.4.12 | 7.4.12 |
| 🐘Packagist | symfony/html-sanitizer | ≥ 8.0.0&&< 8.0.12 | 8.0.12 |
| 🐘Packagist | symfony/symfony | ≥ 6.1.0&&< 6.4.40 | 6.4.40 |
| 🐘Packagist | symfony/symfony | ≥ 7.0.0&&< 7.4.12 | 7.4.12 |
| 🐘Packagist | symfony/symfony | ≥ 8.0.0&&< 8.0.12 | 8.0.12 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/html-sanitizer. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update symfony/html-sanitizer to 6.4.40 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-h5vq-qfcg-4m6p is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-h5vq-qfcg-4m6p is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-h5vq-qfcg-4m6p. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-h5vq-qfcg-4m6p in your dependencies?
O3 detects GHSA-h5vq-qfcg-4m6p across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.