CVE-2026-55517 | Deno is a JavaScript, TypeScript, and WebAssembly runtime. P… | CVSS 4.3 MEDIUM

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.

Metadata

CVE ID: CVE-2026-55517
State: PUBLISHED
Assigner: GitHub_M
Reserved: 2026-06-16 22:44 UTC
Published: 2026-06-23 17:24 UTC
Last updated: 2026-06-23 17:52 UTC
Primary CWE: CWE-248
CWE-248: Uncaught Exception
Vendor / Product: denoland / deno
Sources: cve.org · NVD

Severity & Metrics

4.3 MEDIUM CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

SSVC — CISA Coordinator

Exploitation: none
Automatable: no
Tech. Impact: partial

Affected products (1)

Vendor	Product	Platform	Versions
denoland	deno	—	< 2.7.5

Weakness (CWE)

CWE	Source	Description
CWE-248	cna	CWE-248: Uncaught Exception

CVSS scores (1)

Score	Severity	Version	Source	Vector
4.3	MEDIUM	3.1	cna	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

References (1)

https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf