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VulnerabilityPublished

CVE-2026-55517: denoland deno · Uncaught Exception

Affects denoland denoSource CVE Database V5

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Not known to be exploited · CVSS 4.3 Medium : upgrade to 2.7.5 when convenient.

Data as of 5 Nov 2026, 00:01 UTC

CVSS 3.1 base score
4.3Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 24% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 23 Jun 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

What to do

Upgrade deno and denoland/deno to 2.7.5.

Affected software

ProductAffectedFixed in
denolanddenoAffected
  • <2.7.5
Fixed in
  • 2.7.5
GitHubdenoland/denopkg:github/denoland/denoOther threatsAffected
  • <2.7.5
Fixed in
  • 2.7.5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in Deno version 2.7.5. Users should upgrade to version 2.7.5 or later to remediate this vulnerability. No other mitigations are indicated.

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.

References

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