Missing case-insensitive matching for CSS url function

{
  "id": "093a62156b884bf6bdf9bb115eb10970a8d451b62e06aefd6192d54be3fb59d5",
  "url": "https://osv.dev/vulnerability/RUSTSEC-2026-0373",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Missing case-insensitive matching for CSS url function",
    "summary": "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 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).",
    "evidence": "osv:RUSTSEC-2026-0373",
    "products": [
      {
        "name": {
          "value": "ammonia",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "4.1.8",
            "evidence": "/affected/0/ranges"
          },
          {
            "value": "4.2.4",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "RUSTSEC-2026-0373",
      "aliases": [
        "GHSA-x43w-36pp-96g3",
        "RUSTSEC-2026-0373"
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0.0.0-0"
                },
                {
                  "fixed": "4.1.8"
                },
                {
                  "introduced": "4.2.0"
                },
                {
                  "fixed": "4.2.4"
                }
              ]
            }
          ],
          "package": {
            "name": "ammonia",
            "purl": "pkg:cargo/ammonia",
            "ecosystem": "crates.io"
          },
          "database_specific": {
            "cvss": null,
            "source": "https://github.com/rustsec/advisory-db/blob/osv/crates/RUSTSEC-2026-0373.json",
            "categories": [
              "format-injection"
            ],
            "informational": null
          },
          "ecosystem_specific": {
            "affects": {
              "os": [],
              "arch": [],
              "functions": []
            },
            "affected_functions": null
          }
        }
      ],
      "modified": "2026-10-17T15:30:02.378211969Z",
      "provider": "osv",
      "references": [
        "https://crates.io/crates/ammonia",
        "https://rustsec.org/advisories/RUSTSEC-2026-0373.html",
        "https://github.com/rust-ammonia/ammonia/pull/267"
      ],
      "provider_metadata": {
        "license": "CC0-1.0"
      }
    },
    "related_cves": [],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 362248,
  "published_at": "2026-10-16T12:00:00+00:00"
}