Missing case-insensitive matching for CSS url function

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

not scored

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

URL filtering, such as relative URLs and URL scheme limits, is not always applied when CSS sanitization is used. When the inner URL is quoted, CSS `url("")` is matched case-sensitively, when it should be matched case-insensitively. As a result, while `url("")` gets the intended domain name filtering, `URL("")` does not. The following example shows how an application needs to be configured to trigger this bug. ```rust let mut builder = Builder::new(); // allow inline styles builder.filter_style_properties(hashset!["background-image"]); builder.add_generic_attributes(&["style"]); // notice that "http" URLs aren't allowed builder.url_schemes(["cid"].into()); // attacker-controlled, presumably let cleaned = builder.clean(r#" "#); // this is the expected result assert_eq!(String::from(&cleaned), r#" ok "#); // this is the result that the vulnerable version actually gets assert_eq!(String::from(&cleaned), r#" ok "#); ``` This can be used to inject tracking pixels where the application…

Published by the source

16 Oct 2026, 12:00 UTC

Last modified by the source

17 Oct 2026, 15:30 UTC

Source last checked

23 Oct 2026, 22:04 UTC

1. Revision 1 · created · 24 Oct 2026

   Published from osv record RUSTSEC-2026-0373

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# Patch Next advisory brief: GHSA-x43w-36pp-96g3

Advisory: Missing case-insensitive matching for CSS url function
IDs: GHSA-x43w-36pp-96g3
Record: https://patchnext.com/advisories/rustsec-2026-0373 (revision 1, source checked 23 Oct 2026, 22:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ammonia 4.2.4, 4.1.8. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io ammonia: affected >= 0.0.0-0, < 4.1.8; >= 4.2.0, < 4.2.4; fixed in 4.1.8, 4.2.4

## Suggested inspection (read-only)
- crates.io ammonia: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on ammonia.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/RUSTSEC-2026-0373 (OSV record RUSTSEC-2026-0373 lists affected ranges: crates.io ammonia >=0.0.0-0 =4.2.0 <4.2.4 (fixed))

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