CVE-2026-55517
Medium · 4.3CVSS
4.3
EPSS
0.3%
Published
Jun 23, 2026
CISA due date
—
The record
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 packages
| Ecosystem | Package | Introduced | Fixed |
|---|---|---|---|
| crates.io | deno | 0 | 2.7.5 |
Related vulnerabilities
- GHSA-x2qc-cmh9-f4hf Deno: Denial of service via non-ASCII bytes in WebSocket response headers Same vulnerability
- CVE-2026-49860 Deno is a JavaScript, TypeScript, and WebAssembly runtime. Also affects deno
- CVE-2026-49983 Deno is a JavaScript, TypeScript, and WebAssembly runtime. Also affects deno
- CVE-2026-49401 Deno is a JavaScript, TypeScript, and WebAssembly runtime. Also affects deno
- CVE-2026-49411 Deno is a JavaScript, TypeScript, and WebAssembly runtime. Also affects deno
- CVE-2026-49402 Deno is a JavaScript, TypeScript, and WebAssembly runtime. Also affects deno
- CVE-2026-49440 Deno is a JavaScript, TypeScript, and WebAssembly runtime. Also affects deno
- CVE-2026-49406 Deno is a JavaScript, TypeScript, and WebAssembly runtime. Also affects deno