CVE-2026-55199

HIGHNVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under NVD CVSS v3. EPSS exploit probability: 0.4%, top 67% of all CVEs by exploit prediction. GitHub Security Advisory enrichment pending alignment with NVD CVSS.

Triggered by: NVD CVSS baseline
Sources: epss, ghsa, nvd
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
7.5(medium)
EG Risk
34(Track)
EG Risk 34/100SSVC: Track

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
Severity75% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
33.3%
KEV
Not listed

Published

June 17, 2026

Last Modified

July 14, 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) @ resolute2026-07-16ubuntu
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 7× in last 7d / 93× 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 111 total refreshes for this CVE.

  1. 2026-07-23 14:18 UTCEPSS rescore
  2. 2026-07-23 03:20 UTCEG score recompute▲ 1.60
  3. 2026-07-22 14:08 UTCEPSS rescore
  4. 2026-07-21 15:25 UTCEPSS rescore
  5. 2026-07-20 17:08 UTCEPSS rescore
  6. 2026-07-19 02:29 UTCEPSS rescore
  7. 2026-07-18 10:04 UTCEPSS rescore
  8. 2026-07-16 17:03 UTCEPSS rescore
  9. 2026-07-16 11:37 UTCVendor advisory
  10. 2026-07-16 11:36 UTCGHSA enrichment
  11. 2026-07-15 16:57 UTCEPSS rescore
  12. 2026-07-15 16:57 UTCEPSS rescore
  13. 2026-07-15 12:54 UTCVendor advisory
  14. 2026-07-15 12:54 UTCGHSA enrichment
  15. 2026-07-15 02:00 UTCEPSS rescore
  16. 2026-07-15 02:00 UTCEPSS rescore
  17. 2026-07-14 23:23 UTCNVD updateCVSS v3 → 7.5 · severity → HIGH
  18. 2026-07-14 21:35 UTCMITRE cvelistV5CVSS v3 → 5.9 · severity → MEDIUM
  19. 2026-07-14 11:33 UTCVendor advisory
  20. 2026-07-14 11:32 UTCGHSA enrichment
  21. 2026-07-13 22:31 UTCEPSS rescore
  22. 2026-07-13 12:55 UTCVendor advisory
  23. 2026-07-13 12:55 UTCGHSA enrichment
  24. 2026-07-13 06:13 UTCEPSS rescore
  25. 2026-07-13 06:13 UTCEPSS rescore
Show 75 more
  1. 2026-07-12 14:18 UTCVendor advisory
  2. 2026-07-12 14:18 UTCGHSA enrichment
  3. 2026-07-12 05:46 UTCEPSS rescore
  4. 2026-07-11 15:17 UTCVendor advisory
  5. 2026-07-11 15:17 UTCGHSA enrichment
  6. 2026-07-11 08:27 UTCEPSS rescore
  7. 2026-07-11 08:27 UTCEPSS rescore
  8. 2026-07-10 16:41 UTCVendor advisory
  9. 2026-07-10 16:41 UTCGHSA enrichment
  10. 2026-07-09 19:10 UTCEPSS rescore
  11. 2026-07-09 19:10 UTCEPSS rescore
  12. 2026-07-09 17:56 UTCVendor advisory
  13. 2026-07-09 17:55 UTCGHSA enrichment
  14. 2026-07-08 19:07 UTCVendor advisory
  15. 2026-07-08 19:07 UTCGHSA enrichment
  16. 2026-07-08 15:16 UTCEPSS rescore
  17. 2026-07-08 15:16 UTCEPSS rescore
  18. 2026-07-07 20:18 UTCVendor advisory
  19. 2026-07-07 20:17 UTCGHSA enrichment
  20. 2026-07-07 13:46 UTCEPSS rescore
  21. 2026-07-07 13:46 UTCEPSS rescore
  22. 2026-07-06 21:41 UTCVendor advisory
  23. 2026-07-06 21:41 UTCGHSA enrichment
  24. 2026-07-06 16:27 UTCEPSS rescore
  25. 2026-07-06 16:27 UTCEPSS rescore
  26. 2026-07-06 02:23 UTCEPSS rescore
  27. 2026-07-06 02:23 UTCEPSS rescore
  28. 2026-07-05 21:34 UTCVendor advisory
  29. 2026-07-05 21:34 UTCGHSA enrichment
  30. 2026-07-05 02:31 UTCEPSS rescore
  31. 2026-07-05 02:30 UTCEPSS rescore
  32. 2026-07-04 22:57 UTCVendor advisory
  33. 2026-07-04 22:57 UTCGHSA enrichment
  34. 2026-07-04 06:31 UTCEPSS rescore
  35. 2026-07-04 06:31 UTCEPSS rescore
  36. 2026-07-04 00:19 UTCVendor advisory
  37. 2026-07-04 00:19 UTCGHSA enrichment
  38. 2026-07-03 01:43 UTCVendor advisory
  39. 2026-07-03 01:43 UTCGHSA enrichment
  40. 2026-07-02 03:05 UTCVendor advisory
  41. 2026-07-02 03:05 UTCGHSA enrichment
  42. 2026-07-01 15:07 UTCEPSS rescore
  43. 2026-07-01 04:29 UTCVendor advisory
  44. 2026-07-01 04:29 UTCGHSA enrichment
  45. 2026-06-30 23:22 UTCEPSS rescore
  46. 2026-06-30 05:52 UTCVendor advisory
  47. 2026-06-30 05:52 UTCGHSA enrichment
  48. 2026-06-29 14:06 UTCEPSS rescore
  49. 2026-06-29 14:06 UTCEPSS rescore
  50. 2026-06-29 07:16 UTCVendor advisory
  51. 2026-06-29 07:16 UTCGHSA enrichment
  52. 2026-06-28 14:07 UTCEPSS rescore
  53. 2026-06-28 08:39 UTCVendor advisory
  54. 2026-06-28 08:39 UTCGHSA enrichment
  55. 2026-06-28 04:56 UTCEPSS rescore
  56. 2026-06-28 04:56 UTCEPSS rescore
  57. 2026-06-27 10:03 UTCVendor advisory
  58. 2026-06-27 10:03 UTCGHSA enrichment
  59. 2026-06-27 03:08 UTCEPSS rescore
  60. 2026-06-26 19:41 UTCNVD updateCVSS v3 → 7.5 · severity → HIGH
  61. 2026-06-26 11:27 UTCVendor advisory
  62. 2026-06-26 11:27 UTCGHSA enrichment
  63. 2026-06-25 13:49 UTCEPSS rescore
  64. 2026-06-25 10:32 UTCGHSA enrichment
  65. 2026-06-24 14:05 UTCEPSS rescore
  66. 2026-06-24 11:55 UTCGHSA enrichment
  67. 2026-06-23 21:33 UTCEPSS rescore
  68. 2026-06-23 21:33 UTCEPSS rescore
  69. 2026-06-23 13:16 UTCGHSA enrichment
  70. 2026-06-22 14:39 UTCGHSA enrichment
  71. 2026-06-22 14:25 UTCEPSS rescore
  72. 2026-06-22 14:25 UTCEPSS rescore
  73. 2026-06-21 16:02 UTCGHSA enrichment
  74. 2026-06-21 14:56 UTCEPSS rescore
  75. 2026-06-21 14:56 UTCEPSS rescore

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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 July 14, 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 33.3% 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).
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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