CVE-2026-55517
MEDIUMDeno: Denial of service via non-ASCII bytes in WebSocket response headers
Title source: cnaDescription
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.
References (1)
Core 1
Core References
X_Refsource_Confirm x_refsource_confirm
https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf
Scores
CVSS v3
4.3
EPSS
0.0018
EPSS Percentile
8.2%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
CISA SSVC
Vulnrichment
Exploitation
none
Automatable
no
Technical Impact
partial
Details
CWE
CWE-248
Status
published
Products (2)
deno/deno
< 2.7.5
denoland/deno
< 2.7.5
Published
Jun 23, 2026
Tracked Since
Jun 23, 2026