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: 0.3%, top 76% 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
4.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 4.3Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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
4.3MEDIUMmedium confidence
EG Risk
24
EG Risk 24/100

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity43% × 45%
Exploitation0% × 40%
Automatability30% × 15%
EPSS PROB
0.3%
EPSS %ILE
22nd
KEV
Not listed

Published

June 17, 2026

Last Modified

June 29, 2026

Advisory Details (1)

Auto-updated Jun 23, 2026
Patch available. Sources: github.
githubMentions a patch (unverified)

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 rangeFix by version rangeDependents
deno—
  • every version up to 2.7.5: fixed in 2.7.5
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 7× in last 7d / 26× 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.

Showing the most recent 100 of 137 total refreshes for this CVE.

  1. 2026-10-09 20:07 UTCEPSS rescore
  2. 2026-10-08 17:12 UTCEPSS rescore
  3. 2026-10-07 23:48 UTCEPSS rescore
  4. 2026-10-06 15:18 UTCEPSS rescore
  5. 2026-10-05 17:43 UTCEPSS rescore
  6. 2026-10-04 23:22 UTCEPSS rescore
  7. 2026-10-03 14:26 UTCEPSS rescore
  8. 2026-10-02 17:56 UTCEPSS rescore
  9. 2026-10-02 16:40 UTCOSV refresh
  10. 2026-10-01 19:50 UTCEPSS rescore
  11. 2026-09-30 15:03 UTCEPSS rescore
  12. 2026-09-29 15:22 UTCEPSS rescore
  13. 2026-09-28 13:51 UTCEPSS rescore
  14. 2026-09-27 13:48 UTCEPSS rescore
  15. 2026-09-26 15:59 UTCEPSS rescore
  16. 2026-09-24 14:04 UTCEPSS rescore
  17. 2026-09-23 17:54 UTCEPSS rescore
  18. 2026-09-20 20:16 UTCEPSS rescore
  19. 2026-09-18 19:28 UTCEPSS rescore
  20. 2026-09-17 19:31 UTCEPSS rescore
  21. 2026-09-16 14:08 UTCEPSS rescore
  22. 2026-09-16 05:15 UTCEPSS rescore
  23. 2026-09-15 03:11 UTCEPSS rescore
  24. 2026-09-13 16:47 UTCEPSS rescore
  25. 2026-09-13 14:08 UTCEG score recompute
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  1. 2026-09-11 14:53 UTCEPSS rescore
  2. 2026-09-10 09:35 UTCEPSS rescore
  3. 2026-09-08 22:01 UTCEPSS rescore
  4. 2026-09-07 16:01 UTCEPSS rescore
  5. 2026-09-06 13:47 UTCEPSS rescore
  6. 2026-09-04 05:06 UTCEPSS rescore
  7. 2026-09-02 14:12 UTCEPSS rescore
  8. 2026-09-01 13:54 UTCEPSS rescore
  9. 2026-09-01 04:40 UTCEPSS rescore
  10. 2026-08-30 21:17 UTCEG score recompute
  11. 2026-08-30 19:17 UTCEPSS rescore
  12. 2026-08-30 01:22 UTCEPSS rescore
  13. 2026-08-28 21:41 UTCEPSS rescore
  14. 2026-08-27 14:25 UTCEPSS rescore
  15. 2026-08-26 14:46 UTCEPSS rescore
  16. 2026-08-25 13:49 UTCEPSS rescore
  17. 2026-08-25 04:05 UTCEG score recompute
  18. 2026-08-23 04:01 UTCEG score recompute
  19. 2026-08-23 00:19 UTCEPSS rescore
  20. 2026-08-21 23:49 UTCEPSS rescore
  21. 2026-08-21 07:23 UTCEG score recompute
  22. 2026-08-20 22:55 UTCEPSS rescore
  23. 2026-08-20 08:12 UTCEG score recompute
  24. 2026-08-19 17:04 UTCEPSS rescore
  25. 2026-08-19 08:08 UTCEG score recompute
  26. 2026-08-18 13:48 UTCEPSS rescore
  27. 2026-08-17 13:47 UTCEPSS rescore
  28. 2026-08-17 10:39 UTCEG score recompute
  29. 2026-08-16 14:56 UTCEPSS rescore
  30. 2026-08-16 11:53 UTCEG score recompute
  31. 2026-08-16 02:14 UTCEPSS rescore
  32. 2026-08-15 13:07 UTCEG score recompute
  33. 2026-08-15 01:30 UTCEPSS rescore
  34. 2026-08-14 13:56 UTCEG score recompute
  35. 2026-08-13 22:00 UTCEPSS rescore
  36. 2026-08-12 16:22 UTCEG score recompute
  37. 2026-08-12 13:51 UTCEPSS rescore
  38. 2026-08-11 17:36 UTCEG score recompute
  39. 2026-08-11 00:00 UTCEPSS rescore
  40. 2026-08-09 19:35 UTCEG score recompute
  41. 2026-08-09 13:46 UTCEPSS rescore
  42. 2026-08-08 20:49 UTCEG score recompute
  43. 2026-08-08 16:37 UTCEPSS rescore
  44. 2026-08-07 22:02 UTCEG score recompute
  45. 2026-08-06 23:16 UTCEG score recompute
  46. 2026-08-06 13:47 UTCEPSS rescore
  47. 2026-08-05 23:37 UTCEG score recompute
  48. 2026-08-05 19:17 UTCEPSS rescore
  49. 2026-08-05 00:51 UTCEG score recompute
  50. 2026-08-04 15:10 UTCEPSS rescore
  51. 2026-08-04 10:39 UTCEPSS rescore
  52. 2026-08-04 01:40 UTCEG score recompute
  53. 2026-08-03 10:36 UTCEPSS rescore
  54. 2026-08-02 04:07 UTCEG score recompute
  55. 2026-08-02 02:27 UTCEPSS rescore
  56. 2026-08-01 05:18 UTCEG score recompute
  57. 2026-08-01 04:16 UTCEPSS rescore
  58. 2026-07-31 03:55 UTCEG score recompute
  59. 2026-07-30 16:28 UTCEPSS rescore
  60. 2026-07-30 03:18 UTCEG score recompute
  61. 2026-07-30 01:30 UTCEPSS rescore
  62. 2026-07-29 02:04 UTCEG score recompute
  63. 2026-07-28 15:37 UTCEPSS rescore
  64. 2026-07-27 18:08 UTCEG score recompute
  65. 2026-07-26 19:01 UTCEG score recompute
  66. 2026-07-26 14:54 UTCEPSS rescore
  67. 2026-07-25 14:18 UTCEPSS rescore
  68. 2026-07-24 14:18 UTCEPSS rescore
  69. 2026-07-23 14:18 UTCEPSS rescore
  70. 2026-07-23 03:20 UTCEG score recompute
  71. 2026-07-22 14:08 UTCEPSS rescore
  72. 2026-07-20 17:08 UTCEPSS rescore
  73. 2026-07-19 14:31 UTCEPSS rescore
  74. 2026-07-19 14:31 UTCEPSS rescore
  75. 2026-07-19 02:29 UTCEPSS rescore

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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 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 0.3% probability of exploitation in the next 30 days (22nd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-55517?
CVE-2026-55517 has a CVSS base score of 4.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-55517?
A fix for CVE-2026-55517 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-55517 are linked in the Vendor Advisories panel on this page.

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