How severe is GHSA-hhg7-c65m-h7ff?

No CVSS score has been assigned to GHSA-hhg7-c65m-h7ff yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-hhg7-c65m-h7ff?

GHSA-hhg7-c65m-h7ff affects the following packages: symfony/html-sanitizer (Packagist), symfony/html-sanitizer (Packagist), symfony/html-sanitizer (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist). Ecosystems affected: Packagist.

How do I fix GHSA-hhg7-c65m-h7ff?

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-hhg7-c65m-h7ff is resolved across your whole dependency graph.

How do I detect GHSA-hhg7-c65m-h7ff in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/html-sanitizer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-hhg7-c65m-h7ff if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is GHSA-hhg7-c65m-h7ff actively exploited in the wild?

No public exploit code has been indexed for GHSA-hhg7-c65m-h7ff yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-hhg7-c65m-h7ff?

GHSA-hhg7-c65m-h7ff has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 25th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-hhg7-c65m-h7ff?

GHSA-hhg7-c65m-h7ff is classified as Cross-site Scripting (XSS) (CWE-79), CWE-184 (CWE-184). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was GHSA-hhg7-c65m-h7ff published, and has it been updated?

GHSA-hhg7-c65m-h7ff was published on May 28, 2026 and was last updated on September 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘 Packagist

Not in CISA KEV

Symfony's HtmlSanitizer UrlAttributeSanitizer Omits action/formaction/poster/cite — `javascript`: URI Survives Sanitization (XSS)GHSA-hhg7-c65m-h7ff

Fix: symfony/symfony@26a598f

GHSA-hhg7-c65m-h7ff is a Cross-site Scripting (XSS) vulnerability in symfony/html-sanitizer. A fix is available for symfony/html-sanitizer — see the affected versions and patch details below.

Also known asCVE-2026-45753

Published

May 28, 2026

Updated

Sep 10, 2026

Affected

6 pkgs

Patched

6 / 6

Exploits

None indexed

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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-hhg7-c65m-h7ff.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs25th percentile — riskier than 25% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

6 pkgs affected

🐘symfony/html-sanitizer🐘symfony/html-sanitizer🐘symfony/html-sanitizer🐘symfony/symfony🐘symfony/symfony🐘symfony/symfony

Real-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

symfony/html-sanitizer lets applications sanitise untrusted HTML. UrlAttributeSanitizer is the visitor responsible for validating URL-valued attributes and stripping dangerous schemes from them; it runs on every element regardless of configuration. Whether an attribute is kept is decided by the element/attribute allow-list; validating the scheme of a URL attribute is solely UrlAttributeSanitizer's responsibility.

UrlAttributeSanitizer::getSupportedAttributes() returned only ['src', 'href', 'lowsrc', 'background', 'ping']. The HTML URL-valued attributes action (<form>), formaction (<button>, <input type=image>), poster (<video>) and cite (<blockquote>, <q>, <del>, <ins>) were missing from that list, so DomVisitor never invoked scheme validation for them. As a result, when a configuration admits one of those attributes, a javascript: URI in it survived sanitisation.

Conditions for exploitation

allowSafeElements() is not affected: <form> and the formaction attribute are both flagged unsafe in W3CReference, and allowElement('form') resets the element's attribute list. Reaching the vulnerable attributes requires a deliberately permissive configuration, for example:

<form> + action: allowElement('form', '*'), allowElement('form', ['action', …]), allowElement('form')->allowAttribute('action', 'form'), or the allowStaticElements() preset (whose docblock already warns the output "may still contain other dangerous behaviors");
<button> / <input type=image> + formaction: allowElement(…, '*'), allowAttribute('formaction', …), or allowStaticElements();
<blockquote> / <q> / <del> / <ins> + cite, or <video> + poster: similarly via '*', allowAttribute(), or allowStaticElements().

For the action / formaction cases the victim must additionally submit the form or click the button.

Resolution

UrlAttributeSanitizer now also handles action, formaction, cite and poster. action / formaction / cite are validated against the link schemes (like <a href>, so javascript: is rejected and data: is dropped too); poster is validated against the media schemes (so data: images keep working). The behaviour of <a href> and <img src> is unchanged.

One behaviour change to be aware of: a relative action="/submit" on an allowed <form> is now dropped by default (the same as <a href> / <img src> today); ->allowRelativeLinks() re-enables it.

The patch for this issue is available here for branch 6.4.

Credits

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

Affected Packages

6 total 6 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`symfony/html-sanitizer`	≥ 6.1.0&&< 6.4.40	6.4.40`composer require symfony/html-sanitizer:^6.4.40`
🐘Packagist	`symfony/html-sanitizer`	≥ 7.0.0&&< 7.4.12	7.4.12`composer require symfony/html-sanitizer:^7.4.12`
🐘Packagist	`symfony/html-sanitizer`	≥ 8.0.0&&< 8.0.12	8.0.12`composer require symfony/html-sanitizer:^8.0.12`
🐘Packagist	`symfony/symfony`	≥ 6.1.0&&< 6.4.40	6.4.40`composer require symfony/symfony:^6.4.40`
🐘Packagist	`symfony/symfony`	≥ 7.0.0&&< 7.4.12	7.4.12`composer require symfony/symfony:^7.4.12`
🐘Packagist	`symfony/symfony`	≥ 8.0.0&&< 8.0.12	8.0.12`composer require symfony/symfony:^8.0.12`

Affected Products

1 product · 3 configurations

Application

symfonysensiolabs

≥ 8.0.0 && < 8.0.12

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/html-sanitizer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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-hhg7-c65m-h7ff is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. `UrlAttributeSanitizer` is the visitor responsible for validating URL-valued attributes and stripping dangerous schemes from them; it runs on every element regardless of configuration. Whether an attribute is *kept* is decided by the element/attribute allow-list; validating the *scheme* of a URL attribute is solely `UrlAttributeSanitizer`'s responsibility. `UrlAttributeSanitizer::getSupportedAttributes()` returned only `['src', 'href', 'lowsrc', 'background', 'ping']`. The HTML URL-valued attributes `action`

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Symfony's HtmlSanitizer UrlAttributeSanitizer Omits action/formaction/poster/cite — `javascript`: URI Survives Sanitization (XSS)GHSA-hhg7-c65m-h7ff

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

Real-World Exposure

Description

Description

Conditions for exploitation

Resolution

Credits

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

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