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.

CVSS v3 4.3 MEDIUM

4.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact LOW

Scope UNCHANGED

References

Link	Resource
https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf	Mitigation Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:deno:deno:*:*:*:*:*:*:*:*

History

29 Jun 2026, 13:27

Type	Values Removed	Values Added
CPE		cpe:2.3:a:deno:deno::::::::
First Time		Deno Deno deno
References	~~() https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf -~~	() https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf - Mitigation, Vendor Advisory

23 Jun 2026, 18:18

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-06-23 18:18

Updated : 2026-06-29 13:27

NVD link : CVE-2026-55517

Mitre link : CVE-2026-55517

CVE.ORG link : CVE-2026-55517

JSON object : View

Products Affected

deno

deno

CWE

CWE-248

Uncaught Exception

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