What is GHSA-qc95-4862-92fh?

### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. The configuration methods `allowLinkHosts([...])` and `allowLinkSchemes([...])` are intended to restrict ` ` targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for ` ` etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, `UrlSanitizer::parse()` parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises `\` to `/` before parsing the authority of "special"

How severe is GHSA-qc95-4862-92fh?

No CVSS score has been assigned to GHSA-qc95-4862-92fh yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-qc95-4862-92fh?

GHSA-qc95-4862-92fh 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-qc95-4862-92fh?

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-qc95-4862-92fh is resolved across your whole dependency graph.

How do I detect GHSA-qc95-4862-92fh 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-qc95-4862-92fh if there is no patch (or I can't update yet)?

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.

Is GHSA-qc95-4862-92fh actively exploited in the wild?

No public exploit code has been indexed for GHSA-qc95-4862-92fh 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-qc95-4862-92fh?

GHSA-qc95-4862-92fh 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-qc95-4862-92fh?

GHSA-qc95-4862-92fh is classified as CWE-184 (CWE-184), CWE-436 (CWE-436). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-qc95-4862-92fh published, and has it been updated?

GHSA-qc95-4862-92fh was published on May 27, 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 has an HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URL-Parser Differentials and <area> MisclassificationGHSA-qc95-4862-92fh

GHSA-qc95-4862-92fh is a CWE-184 vulnerability in symfony/html-sanitizer. A fix is available for symfony/html-sanitizer — see the affected versions and patch details below.

Also known asCVE-2026-45066

Published

May 27, 2026

Updated

Sep 10, 2026

Affected

6 pkgs

Patched

6 / 6

Exploits

None indexed

Exploitation data as of Oct 8, 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-qc95-4862-92fh.

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. The configuration methods allowLinkHosts([...]) and allowLinkSchemes([...]) are intended to restrict <a href> targets to an allowlist of hosts/schemes; allowMediaHosts() / allowMediaSchemes() do the same for <img src> etc.

Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, UrlSanitizer::parse() parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises \ to / before parsing the authority of "special" schemes; so an input like https://evil\@trusted.com/ parses with host trusted.com server-side but navigates to https://evil/ in the browser. Second, WHATWG collapses any run of / after the scheme into //, while RFC-3986 does not; so https:/evil.com/ and https:///evil.com/ parse as host-less (skipping the host allowlist) but resolve to evil.com in the browser. Third, UrlAttributeSanitizer checks 'a' === $element to route to the link policy and falls through to the media policy otherwise, but <area> is a navigable hyperlink equivalent to <a>; so <area href> was sanitised against the media policy (which typically allows data: and may have no host allowlist), bypassing allowLinkHosts() / allowLinkSchemes() entirely.

Resolution

UrlSanitizer::sanitize() now rejects URLs that contain a backslash or that use a special scheme (http, https, ftp, ws, wss) followed by a single slash or three slashes before parsing, eliminating the parser-differential bypasses. UrlAttributeSanitizer now applies the link policy to both <a> and <area> elements.

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

Credits

Symfony would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and 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-qc95-4862-92fh 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.

Frequently Asked Questions

### Description `symfony/html-sanitizer` lets applications sanitise untrusted HTML. The configuration methods `allowLinkHosts([...])` and `allowLinkSchemes([...])` are intended to restrict `<a href>` targets to an allowlist of hosts/schemes; `allowMediaHosts()` / `allowMediaSchemes()` do the same for `<img src>` etc. Three distinct bypasses allow a content author to smuggle off-allowlist URLs past these checks. First, `UrlSanitizer::parse()` parses the input following RFC-3986, while browsers follow the WHATWG URL Standard which normalises `\` to `/` before parsing the authority of "special"

O3 Security · Impact-Aware SCA

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Find it across Packagist, including transitive dependencies.

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Symfony has an HtmlSanitizer allowLinkHosts() / allowMediaHosts() Bypass via URL-Parser Differentials and <area> MisclassificationGHSA-qc95-4862-92fh

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

Real-World Exposure

Description

Description

Resolution

Credits

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is GHSA-qc95-4862-92fh in your dependencies?