CVE-2026-55517

MEDIUMPre-NVD 4.34.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 4.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 92% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
4.3
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 4.3Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
4.3
EG Score
4.3(medium)
EPSS
8.1%
KEV
Not listed

Published

June 17, 2026

Last Modified

June 29, 2026

Advisory Details (1)

Auto-updated Jun 23, 2026
Patch available. Sources: github.
github Patch Available

Denial of service via non-ASCII bytes in WebSocket response headers · Advisory · denoland/deno · GitHub

https://github.com/denoland/deno/security/advisories/GHSA-x2qc-cmh9-f4hf

Vendor Advisories for CVE-2026-55517(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(1 across 1 ecosystem)
crates.io(1)
PackageVulnerable rangeFixed inDependents
deno—2.7.5—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 17× in last 7d / 39× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-06 22:21 UTCEG score recompute
  2. 2026-07-06 16:27 UTCEPSS rescore
  3. 2026-07-06 16:27 UTCEPSS rescore
  4. 2026-07-06 02:23 UTCEPSS rescore
  5. 2026-07-06 02:23 UTCEPSS rescore
  6. 2026-07-05 23:23 UTCEG score recompute
  7. 2026-07-05 02:31 UTCEPSS rescore
  8. 2026-07-05 02:30 UTCEPSS rescore
  9. 2026-07-05 00:35 UTCEG score recompute
  10. 2026-07-04 06:31 UTCEPSS rescore
  11. 2026-07-04 06:31 UTCEPSS rescore
  12. 2026-07-04 01:48 UTCEG score recompute
  13. 2026-07-03 03:01 UTCEG score recompute
  14. 2026-07-02 04:13 UTCEG score recompute
  15. 2026-07-01 15:07 UTCEPSS rescore
  16. 2026-07-01 05:25 UTCEG score recompute
  17. 2026-06-30 23:22 UTCEPSS rescore
  18. 2026-06-30 06:37 UTCEG score recompute
  19. 2026-06-29 14:06 UTCEPSS rescore
  20. 2026-06-29 14:06 UTCEPSS rescore
  21. 2026-06-29 07:49 UTCEG score recompute
  22. 2026-06-28 14:07 UTCEPSS rescore
  23. 2026-06-28 09:01 UTCEG score recompute
  24. 2026-06-28 04:56 UTCEPSS rescore
  25. 2026-06-28 04:56 UTCEPSS rescore
Show 14 more
  1. 2026-06-27 10:15 UTCEG score recompute
  2. 2026-06-27 03:08 UTCEPSS rescore
  3. 2026-06-26 11:27 UTCEG score recompute
  4. 2026-06-25 13:49 UTCEPSS rescore
  5. 2026-06-25 09:32 UTCEG score recompute
  6. 2026-06-24 14:05 UTCEPSS rescore
  7. 2026-06-24 10:45 UTCEG score recompute
  8. 2026-06-23 11:57 UTCEG score recompute
  9. 2026-06-22 13:06 UTCEG score recompute
  10. 2026-06-21 14:19 UTCEG score recompute
  11. 2026-06-20 15:32 UTCEG score recompute
  12. 2026-06-19 16:44 UTCEG score recompute
  13. 2026-06-18 17:55 UTCEG score recompute
  14. 2026-06-17 19:06 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-55517?
CVE-2026-55517 is a medium vulnerability published on June 17, 2026. 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…
When was CVE-2026-55517 disclosed?
CVE-2026-55517 was first published in the National Vulnerability Database on June 17, 2026, with the most recent update on June 29, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-55517 actively exploited?
CVE-2026-55517 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 8.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-55517?
CVE-2026-55517 has a CVSS v3 base score of 4.3 (NVD).
How do I remediate CVE-2026-55517?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-55517, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-55517

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