4.3

CVE-2026-55517: deno Uncaught Exception

CVSS: 4.3v3.1MediumAnalyzed
AliasesGHSA-x2qc-cmh9-f4hf
Published 23-06-2026Last modified 23-06-2026
Open JSON

Vulnerability summary

CVE-2026-55517 is a medium (CVSS 4.3) Uncaught Exception vulnerability in deno. EPSS estimates a 0.32% chance of exploitation in the next 30 days, higher than 23% of scored vulnerabilities.

Overall risk
17/100
0100
Low · default modelHow is this calculated?
CVSS score
4.3/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.32%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 23-06-2026
    PublishedVulnerability first disclosed.
  2. 23-06-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

3 scores · 3 sources · 1 version

EPSS trend

Probability

0.32%

Chance of exploitation in the next 30 days

Percentile

23%

Versus all other CVEs

30-day change

0.00 pp

From 0.32% on 20-09-2026

20-09-202620-10-2026
EPSS score
0.32%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Crates.Io1 product
  • deno< 2.7.5
Deno1 product
Denoland1 product

3 vendors · 3 products

References

2 links