Advisory details:
github_osv / GHSA-hhg7-c65m-h7ff
| Advisory ID | github_osv/GHSA-hhg7-c65m-h7ff |
| Aliases |
CVE-2026-45753
|
| Summary | Symfony's HtmlSanitizer UrlAttributeSanitizer Omits action/formaction/poster/cite — `javascript`: URI Survives Sanitization (XSS) ### 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](https://github.com/symfony/symfony/commit/26a598fcfc4f903cc55ff202f642ee621839825e) 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. |
| Status | Published |
| Exploitability | 0.5 |
| Weighted Severity | 1.1 |
| Risk | 0.6 |
| Affected and Fixed Packages | Package Details |
| Introduced and Fixed Package Commit Patches | Package Commit Patches Details |
| System | Score | Found at |
|---|---|---|
| cvssv4 | 1.2 | https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-hhg7-c65m-h7ff/GHSA-hhg7-c65m-h7ff.json |
| generic_textual | LOW |
No EPSS data available for this advisory.
| Patch URL | |
|---|---|
| There are no known patches. | |
| Attack Vector (AV) | Attack Complexity (AC) | Attack Requirements (AT) | Privileges Required (PR) | User Interaction (UI) | Vulnerable System Impact Confidentiality (VC) | Vulnerable System Impact Integrity (VI) | Vulnerable System Impact Availability (VA) | Subsequent System Impact Confidentiality (SC) | Subsequent System Impact Integrity (SI) | Subsequent System Impact Availability (SA) |
|---|---|---|---|---|---|---|---|---|---|---|
network adjacent local physical |
low high |
none present |
none low high |
none passive active |
high low none |
high low none |
high low none |
high low none |
high low none |
high low none |
Vector: SSVCv2/E:N/A:N/T:P/P:M/B:A/M:M/D:T/2026-07-14T18:39:22Z/
Decision: Track
Source URL: https://github.com/cisagov/vulnrichment/blob/develop/2026/45xxx/CVE-2026-45753.json
Source Advisory: vulnrichment/CVE-2026-45753
[{'Exploitation': 'none'},
{'Automatable': 'no'},
{'Technical Impact': 'partial'},
{'Mission Prevalence': 'minimal'},
{'Public Well-being Impact': 'material'},
{'Mission & Well-being': 'medium'}]