{"schema_version":"1.9.0","id":"RUSTSEC-2026-0373","published":"2026-10-16T12:00:00Z","modified":"2026-10-17T15:30:02.378211969Z","aliases":["GHSA-x43w-36pp-96g3"],"summary":"Missing case-insensitive matching for CSS url function","details":"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).","affected":[{"package":{"name":"ammonia","ecosystem":"crates.io","purl":"pkg:cargo/ammonia"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.0.0-0"},{"fixed":"4.1.8"},{"introduced":"4.2.0"},{"fixed":"4.2.4"}]}],"ecosystem_specific":{"affected_functions":null,"affects":{"arch":[],"functions":[],"os":[]}},"database_specific":{"categories":["format-injection"],"cvss":null,"informational":null,"source":"https://github.com/rustsec/advisory-db/blob/osv/crates/RUSTSEC-2026-0373.json"}}],"references":[{"type":"PACKAGE","url":"https://crates.io/crates/ammonia"},{"type":"ADVISORY","url":"https://rustsec.org/advisories/RUSTSEC-2026-0373.html"},{"type":"WEB","url":"https://github.com/rust-ammonia/ammonia/pull/267"}],"database_specific":{"license":"CC0-1.0"}}