{"id":"CVE-2026-55517","aliases":["GHSA-x2qc-cmh9-f4hf"],"url":"https://o3.security/vulnerability/CVE-2026-55517","summary":"Deno: Denial of service via non-ASCII bytes in WebSocket response headers","details":"Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.7.5, a Deno program that opens a client WebSocket connection could be crashed by the remote server. While handling the WebSocket handshake response, Deno parsed the Sec-WebSocket-Protocol and Sec-WebSocket-Extensions response headers in a way that assumed their bytes were always printable ASCII. A response header containing non-visible-ASCII bytes (0x80-0xFF) caused a panic that aborted the entire Deno process. This vulnerability is fixed in 2.7.5.","published":"2026-06-23T17:24:59.498Z","modified":"2026-08-12T03:51:49.134302786Z","cvss":{"score":4.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L"},"epss":{"score":0.00315,"percentile":0.2387,"asOf":"2026-09-01"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"crates.io","name":"deno","fixedVersion":"2.7.5"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55517.json"},{"type":"ADVISORY","url":"https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55517"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:49.134302786Z"}}