CVE-2026-55199

HIGHNVD 7.55.9▼
EchelonGraph scoreMEDIUM confidence

Score 5.9 from GitHub Security Advisory (severity: HIGH) published 2026-06-17. NVD baseline CVSS 7.5; sources differ by 1.6.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 4 sources updated this week
7.5
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 7.5Exploit: NoneExposed: 0

A fix is available — apply it.

libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.

CVSS v3
7.5
EG Score
5.9(medium)
EPSS
32.7%
KEV
Not listed

Published

June 17, 2026

Last Modified

June 26, 2026

Advisory Details (3)

Auto-updated Jun 17, 2026
Upstream fix merged — awaiting tagged release. Sources: github_commit, github_pr.
generic

libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler | Advisories | VulnCheck

https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler
github_pr

packet.c: check _libssh2_get_string() return in EXT_INFO handler

Upstream fix in progress (PR #1864 · libssh2/libssh2, state=closed)

https://github.com/libssh2/libssh2/pull/1864
github_commit

commit 17626857d20b (libssh2/libssh2)

Fix landed in libssh2/libssh2 commit 17626857d20b — awaiting tagged release

https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4

Vendor Advisories for CVE-2026-55199(3)

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

Patch Availability(2)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulibssh2-1t64 (1.11.1-1ubuntu0.26.04.2) @ resolute2026-07-06ubuntu
redhatlibssh2-main-1.11.1-8.hum12026-06-25redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

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

Additional Vendor Advisories

(1)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 31× in last 7d / 85× 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 21:41 UTCEG score recompute
  2. 2026-07-06 21:41 UTCVendor advisory
  3. 2026-07-06 21:41 UTCGHSA enrichment
  4. 2026-07-06 16:27 UTCEPSS rescore
  5. 2026-07-06 16:27 UTCEPSS rescore
  6. 2026-07-06 02:23 UTCEPSS rescore
  7. 2026-07-06 02:23 UTCEPSS rescore
  8. 2026-07-05 21:34 UTCEG score recompute
  9. 2026-07-05 21:34 UTCVendor advisory
  10. 2026-07-05 21:34 UTCGHSA enrichment
  11. 2026-07-05 02:31 UTCEPSS rescore
  12. 2026-07-05 02:30 UTCEPSS rescore
  13. 2026-07-04 22:57 UTCEG score recompute
  14. 2026-07-04 22:57 UTCVendor advisory
  15. 2026-07-04 22:57 UTCGHSA enrichment
  16. 2026-07-04 06:31 UTCEPSS rescore
  17. 2026-07-04 06:31 UTCEPSS rescore
  18. 2026-07-04 00:19 UTCEG score recompute
  19. 2026-07-04 00:19 UTCVendor advisory
  20. 2026-07-04 00:19 UTCGHSA enrichment
  21. 2026-07-03 01:43 UTCEG score recompute
  22. 2026-07-03 01:43 UTCVendor advisory
  23. 2026-07-03 01:43 UTCGHSA enrichment
  24. 2026-07-02 03:05 UTCEG score recompute
  25. 2026-07-02 03:05 UTCVendor advisory
Show 60 more
  1. 2026-07-02 03:05 UTCGHSA enrichment
  2. 2026-07-01 15:07 UTCEPSS rescore
  3. 2026-07-01 04:29 UTCEG score recompute
  4. 2026-07-01 04:29 UTCVendor advisory
  5. 2026-07-01 04:29 UTCGHSA enrichment
  6. 2026-06-30 23:22 UTCEPSS rescore
  7. 2026-06-30 05:52 UTCEG score recompute
  8. 2026-06-30 05:52 UTCVendor advisory
  9. 2026-06-30 05:52 UTCGHSA enrichment
  10. 2026-06-29 14:06 UTCEPSS rescore
  11. 2026-06-29 14:06 UTCEPSS rescore
  12. 2026-06-29 07:16 UTCEG score recompute
  13. 2026-06-29 07:16 UTCVendor advisory
  14. 2026-06-29 07:16 UTCGHSA enrichment
  15. 2026-06-28 14:07 UTCEPSS rescore
  16. 2026-06-28 08:39 UTCEG score recompute
  17. 2026-06-28 08:39 UTCVendor advisory
  18. 2026-06-28 08:39 UTCGHSA enrichment
  19. 2026-06-28 04:56 UTCEPSS rescore
  20. 2026-06-28 04:56 UTCEPSS rescore
  21. 2026-06-27 10:03 UTCEG score recompute
  22. 2026-06-27 10:03 UTCVendor advisory
  23. 2026-06-27 10:03 UTCGHSA enrichment
  24. 2026-06-27 03:08 UTCEPSS rescore
  25. 2026-06-26 19:41 UTCNVD updateCVSS v3 → 7.5 · severity → HIGH
  26. 2026-06-26 11:27 UTCEG score recompute
  27. 2026-06-26 11:27 UTCVendor advisory
  28. 2026-06-26 11:27 UTCGHSA enrichment
  29. 2026-06-25 13:49 UTCEPSS rescore
  30. 2026-06-25 10:32 UTCEG score recompute
  31. 2026-06-25 10:32 UTCGHSA enrichment
  32. 2026-06-24 14:05 UTCEPSS rescore
  33. 2026-06-24 11:55 UTCEG score recompute
  34. 2026-06-24 11:55 UTCGHSA enrichment
  35. 2026-06-23 21:33 UTCEPSS rescore
  36. 2026-06-23 21:33 UTCEPSS rescore
  37. 2026-06-23 13:16 UTCEG score recompute
  38. 2026-06-23 13:16 UTCGHSA enrichment
  39. 2026-06-22 14:39 UTCEG score recompute
  40. 2026-06-22 14:39 UTCGHSA enrichment
  41. 2026-06-22 14:25 UTCEPSS rescore
  42. 2026-06-22 14:25 UTCEPSS rescore
  43. 2026-06-21 16:02 UTCEG score recompute
  44. 2026-06-21 16:02 UTCGHSA enrichment
  45. 2026-06-21 14:56 UTCEPSS rescore
  46. 2026-06-21 14:56 UTCEPSS rescore
  47. 2026-06-21 01:59 UTCEPSS rescore
  48. 2026-06-21 01:59 UTCEPSS rescore
  49. 2026-06-20 17:09 UTCEG score recompute
  50. 2026-06-20 17:08 UTCGHSA enrichment
  51. 2026-06-19 19:26 UTCEPSS rescore
  52. 2026-06-19 19:26 UTCEPSS rescore
  53. 2026-06-19 18:32 UTCEG score recompute
  54. 2026-06-19 18:32 UTCGHSA enrichment
  55. 2026-06-18 19:54 UTCEG score recompute
  56. 2026-06-18 19:53 UTCGHSA enrichment
  57. 2026-06-18 17:52 UTCEPSS rescore
  58. 2026-06-18 17:52 UTCEPSS rescore
  59. 2026-06-17 21:16 UTCEG score recompute
  60. 2026-06-17 21:16 UTCNVD updatefirst tracked

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2026-55199?
CVE-2026-55199 is a high vulnerability published on June 17, 2026. libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSHMSGEXTINFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set…
When was CVE-2026-55199 disclosed?
CVE-2026-55199 was first published in the National Vulnerability Database on June 17, 2026, with the most recent update on June 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-55199 actively exploited?
CVE-2026-55199 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 32.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-55199?
CVE-2026-55199 has a CVSS v3 base score of 7.5 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 5.9.
How do I remediate CVE-2026-55199?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-55199, 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.

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