What is CVE-2026-55517?

CVE-2026-55517 is a medium-severity vulnerability in Deno, classified under CWE-248. CVSS score: 4.3/10. Published 2026-06-23.

How severe is CVE-2026-55517?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Vulnerability in Deno

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-…

EPSS: 0.002 (8.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L.

Affected products

Deno
Denoland Deno — versions < 2.7.5

Weakness classification (CWE)

CWE-248

References

security-advisories@github.com (x_refsource_CONFIRM, Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-55517?: CVE-2026-55517 is a medium-severity vulnerability in Deno, classified under CWE-248. CVSS score: 4.3/10. Published 2026-06-23.
How severe is CVE-2026-55517?: Medium severity. CVSS v3 base score is 4.3 out of 10.