CVE-2026-55517

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.

• CWE-248

• https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hfMitigation, Vendor Advisory

Published

Jun 23, 2026

Last Modified

Jun 29, 2026

Status

Analyzed

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