{"id":"CVE-2026-9675","aliases":["GHSA-38rv-x7px-6hhq"],"url":"https://o3.security/vulnerability/CVE-2026-9675","summary":"undici WebSocket client vulnerable to denial of service via cumulative fragment bypass","details":"## Impact\n\nThe undici WebSocket client enforces `maxPayloadSize` per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.\n\nAffected applications are those using the undici WebSocket client (`new WebSocket(...)`) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.\n\nThis is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the `maxPayloadSize` feature and is also unaffected.\n\n## Patches\n\nUpgrade to undici >= 8.5.0.\n\n## Workarounds\n\nNo workaround is available. The fix must be applied through an upgrade.","published":"2026-06-17T16:20:32.548Z","modified":"2026-08-12T03:51:40.656296970Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.00426,"percentile":0.36043,"asOf":"2026-09-12"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"undici","fixedVersion":"8.5.0"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/9xxx/CVE-2026-9675.json"},{"type":"ADVISORY","url":"https://github.com/nodejs/undici/security/advisories/GHSA-38rv-x7px-6hhq"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-9675"},{"type":"PACKAGE","url":"https://github.com/nodejs/undici"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:40.656296970Z"}}