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Findings

Vulnerability · RUSTSEC-2026-0373

Missing case-insensitive matching for CSS url function

Published Oct 16, 2026 · corrected/updated Oct 17, 2026 · evidence confidence medium

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 is matched case-sensitively, when it should be matched case-insensitively. As a result, while gets the intended domain name filtering, does not. The following example shows how an application needs to be configured to trigger this bug. This can be used to inject tracking pixels where the application intended to prevent them. It does not allow XSS, and its usefulness for data exfiltration is limited. --- This vulnerability was reported by [Louis Li](https://github.com/zhixuli0406).

Grounded briefings

Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.

Executive

RUSTSEC-2026-0373 is a unknown public vulnerability record for this product. It is not currently listed in the CISA Known Exploited catalog. Check the linked vendor or CERT advisories for patch status. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.

System administrator

Identify whether this product is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: ammonia (0.0.0-0 → 4.1.8). Check the linked vendor or CERT advisories for patch status. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.

Security analyst

Signals on file: no CVSS/EPSS yet. It is not currently listed in the CISA Known Exploited catalog. Sources contributing to this record: github, osv. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.

Exploitation and remediation

  • Exploitation evidence

    Not listed as known exploited in CISA KEV. Not in CISA KEV or VulnCheck KEV.

  • Patch and remediation

    No required-action text is stored yet. Use the vendor or CERT links in Sources for patch availability.

  • Safe detection guidance

    Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 16, 2026 · GitHub Advisory Database

    Detected

    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 is matched case-sensitively, when it should be matched case-insensitively. As a result, while gets the intended domain name filtering, does not. The following example shows how an application needs to be configured to trigger this bug. This can be used

  2. Oct 17, 2026 · GitHub Advisory Database

    Fix available

    ammonia fixed in 4.1.8

  3. Oct 17, 2026 · GitHub Advisory Database

    Fix available

    ammonia fixed in 4.1.8

  4. Oct 17, 2026 · GitHub Advisory Database

    Updated

    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 is matched case-sensitively, when it should be matched case-insensitively. As a result, while gets the intended domain name filtering, does not. The following example shows how an application needs to be configured to trigger this bug. This can be used

Affected

  • crates.io ammonia0.0.0-0 → 4.1.8

Sources

References