WebSocket Protocol Vulnerability in Deno Runtime from DenoLand
CVE-2026-55517

4.3MEDIUM

Key Information:

Vendor

Denoland

Status
Deno
Vendor
CVE Published:
23 June 2026

What is CVE-2026-55517?

A vulnerability in the Deno runtime allows a client program that opens WebSocket connections to be crashed by a malicious remote server. Before version 2.7.5, Deno improperly handled the Sec-WebSocket-Protocol and Sec-WebSocket-Extensions headers during the WebSocket handshake. If these headers contained non-visible ASCII bytes (0x80-0xFF), it could result in a panic that terminated the entire Deno process. This issue has been resolved in version 2.7.5.

Affected Version(s)

deno < 2.7.5

References

https://github.com/denoland/deno/security/advisories/GHSA...
x_refsource_CONFIRM

CVSS V3.1

Score:
4.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
Required
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.