{"aliases":["GHSA-x43w-36pp-96g3"],"categories":["format-injection"],"crate":"ammonia","cves":[],"cvss":0.0,"database_specific":{"severity":""},"date":"2026-10-16","deb_packages":[{"crate_name":"ammonia","deb_name":"librust-ammonia-dev","version":"4.2.3-1"}],"description":"URL filtering, such as relative URLs and URL scheme limits,\nis not always applied when CSS sanitization is used.\n\nWhen the inner URL is quoted, CSS `url(\"\")` is matched case-sensitively,\nwhen it should be matched case-insensitively.\nAs a result, while `url(\"\")` gets the intended domain name filtering,\n`URL(\"\")` does not.\n\nThe following example shows how an application needs to be configured\nto trigger this bug.\n\n```rust\nlet mut builder = Builder::new();\n// allow inline styles\nbuilder.filter_style_properties(hashset![\"background-image\"]);\nbuilder.add_generic_attributes(&[\"style\"]);\n// notice that \"http\" URLs aren't allowed\nbuilder.url_schemes([\"cid\"].into());\n\n// attacker-controlled, presumably\nlet cleaned = builder.clean(r#\"<div style='background:URL(\"https://evil.com/ping\");'>\"#);\n\n// this is the expected result\nassert_eq!(String::from(&cleaned), r#\"<div style=\"\">ok</p>\"#);\n\n// this is the result that the vulnerable version actually gets\nassert_eq!(String::from(&cleaned), r#\"<div style=\"background-image:URL(&quot;https://evil.com/ping&quot;);\">ok</p>\"#);\n```\n\nThis can be used to inject tracking pixels where the application intended to prevent them.\nIt does not allow XSS, and its usefulness for data exfiltration is limited.\n\n---\n\nThis vulnerability was reported by [Louis Li](https://github.com/zhixuli0406).","id":"RUSTSEC-2026-0373","keywords":["css","html"],"patched_versions":[">=4.2.4",">=4.1.8, <4.2.0"],"source":"debian_rustsec","title":"Missing case-insensitive matching for CSS url function","url":"https://github.com/rust-ammonia/ammonia/pull/267"}