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Medium · 4.3 CVE-2026-55517 EUVD-2026-38549GHSA-x2qc-cmh9-f4hf

Deno: Denial of service via non-ASCII bytes in WebSocket response headers

Published Jun 23, 2026 · Updated Jun 23, 2026 · Assigned by GitHub_M

Description

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.

Affected products

VendorProductAffectedFixed
denoland deno < 2.7.5 —

Affected packages

EcosystemPackageAffectedFixedRecord
crates.io deno < 2.7.5 2.7.5 GHSA-x2qc-cmh9-f4hf

References