CVE-2026-66033

HIGHPre-NVD 7.57.5—
EchelonGraph scoreHIGH confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-07-24. the CNA's CVSS baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cna:vulncheck, epss, ghsa
Trending — Patch released this week
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.5Exploit: None knownExposed: 0

A fix is available — apply it.

libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.

CVSS v3
7.5
EG Score
7.5(high)
EG Risk
49(Track)
EG Risk 49/100SSVC: 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%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
31%
KEV
Not listed

Published

July 24, 2026

Last Modified

July 28, 2026

Advisory Details (3)

Auto-updated Jul 24, 2026
Upstream fix merged — awaiting tagged release. Sources: github_commit, github_pr.
generic

libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation | Advisories | VulnCheck

https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation
github_pr

openssl: fix potential OOB read/write with AES-GCM in `ssh2_cipher_crypt()`

Upstream fix in progress (PR #2401 · libssh2/libssh2, state=closed)

https://github.com/libssh2/libssh2/pull/2401
github_commit

commit a2ed82d40964 (libssh2/libssh2)

Fix landed in libssh2/libssh2 commit a2ed82d40964 — awaiting tagged release

https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6

Vendor Advisories for CVE-2026-66033(3)

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

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatlibssh2-main-1.11.1-10.2.hum12026-07-27redhat

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(2)

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

Data Freshness Timeline

(refreshed 21× in last 7d / 21× 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. 2026-07-28 01:30 UTCEG score recompute
  2. 2026-07-28 01:30 UTCVendor advisory
  3. 2026-07-28 01:30 UTCGHSA enrichment
  4. 2026-07-27 17:20 UTCEG score recompute
  5. 2026-07-27 17:20 UTCGHSA enrichment
  6. 2026-07-27 17:02 UTCEG score recompute
  7. 2026-07-27 17:02 UTCGHSA enrichment
  8. 2026-07-27 14:14 UTCEPSS rescore
  9. 2026-07-27 11:56 UTCGHSA enrichment
  10. 2026-07-27 00:57 UTCEG score recompute
  11. 2026-07-27 00:57 UTCGHSA enrichment
  12. 2026-07-26 14:54 UTCEPSS rescore
  13. 2026-07-26 14:54 UTCEPSS rescore
  14. 2026-07-26 13:56 UTCEG score recompute
  15. 2026-07-26 13:56 UTCGHSA enrichment
  16. 2026-07-26 02:56 UTCEG score recompute
  17. 2026-07-26 02:56 UTCGHSA enrichment
  18. 2026-07-25 14:18 UTCEPSS rescore
  19. 2026-07-25 14:18 UTCEPSS rescore
  20. 2026-07-24 16:53 UTCEG score recompute
  21. 2026-07-24 16:52 UTCMITRE cvelistV5first tracked

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2026-66033?
CVE-2026-66033 is a high vulnerability published on July 24, 2026. libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2ciphercrypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit…
When was CVE-2026-66033 disclosed?
CVE-2026-66033 was first published in the National Vulnerability Database on July 24, 2026, with the most recent update on July 28, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-66033 actively exploited?
CVE-2026-66033 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 68.7% of all scored CVEs.
What is the CVSS score of CVE-2026-66033?
CVE-2026-66033 has a CVSS v4.0 base score of 7.5 (CNA self-assessment; NVD's own analysis pending).
How do I remediate CVE-2026-66033?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-66033, 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

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