CVE-2026-55517 json
Deno: Denial of service via non-ASCII bytes in WebSocket response headers
published 4mo ago modified 17d ago also EUVD-2026-38549 , GHSA-x2qc-cmh9-f4hf , JLSEC-2026-1167
- cvss
- 4.3
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.3%
- EPSS 0.3% chance of exploitation in 30 days, percentile 24%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- crates.io deno 2.7.5
- julia Deno_jll 2.8.1+0
- deno deno 2.7.5
- deno deno_runtime 2.7.5
- deno serde_v8 2.7.5
Is CVE-2026-55517 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 4mo ago
Exploit prediction
0.32% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-11).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 4.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L |
| GitHub | 3.1 | 4.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L |
| OSV | 3.1 | 4.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| crates.io | deno | <2.7.5 |
2.7.5 |
| julia | Deno_jll | <2.8.1+0 |
2.8.1+0 |
Affected products
- denoland deno
Classification
- Weakness
-
- CWE-248 Uncaught Exception
References
-
github.com
/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf
web, mitigation, vendor-advisory
-
github.com
/denoland/deno
package
-
github.com
/advisories/GHSA-x2qc-cmh9-f4hf
web
Sources
- CVE List CVE-2026-55517
- GitHub Advisory GHSA-x2qc-cmh9-f4hf
- NVD CVE-2026-55517
- OSV JLSEC-2026-1167
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.