CVE-2026-66035

HIGHPre-NVD 7.57.5—
EchelonGraph scoreHIGH confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-07-24. a secondary CVSS source baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
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 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.

CVSS v3
7.5
EG Score
7.5(high)
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 PROB
0%
EPSS %ILE
24%
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 Heap Buffer Overflow via ETM Cipher Negotiation | Advisories | VulnCheck

https://www.vulncheck.com/advisories/libssh2-heap-buffer-overflow-via-etm-cipher-negotiation
github_pr

transport: fix potential heap overflow on ETM decrypt

Upstream fix in progress (PR #2198 · libssh2/libssh2, state=closed)

https://github.com/libssh2/libssh2/pull/2198
github_commit

commit 42e33d81577e (libssh2/libssh2)

Fix landed in libssh2/libssh2 commit 42e33d81577e — awaiting tagged release

https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4

Vendor Advisories for CVE-2026-66035(2)

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-1.11.1-10.3.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(1)

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

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 27× in last 7d / 27× 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. 2026-07-29 15:37 UTCVendor advisory
  2. 2026-07-29 15:37 UTCGHSA enrichment
  3. 2026-07-29 04:05 UTCVendor advisory
  4. 2026-07-29 04:04 UTCGHSA enrichment
  5. 2026-07-28 16:31 UTCEG score recompute
  6. 2026-07-28 16:31 UTCVendor advisory
  7. 2026-07-28 16:31 UTCGHSA enrichment
  8. 2026-07-28 15:37 UTCEPSS rescore
  9. 2026-07-28 13:05 UTCVendor advisory
  10. 2026-07-28 13:04 UTCGHSA enrichment
  11. 2026-07-28 01:30 UTCVendor advisory
  12. 2026-07-28 01:30 UTCGHSA enrichment
  13. 2026-07-27 15:04 UTCEG score recompute
  14. 2026-07-27 15:04 UTCGHSA enrichment
  15. 2026-07-27 14:14 UTCEPSS rescore
  16. 2026-07-27 02:01 UTCEG score recompute
  17. 2026-07-27 02:01 UTCGHSA enrichment
  18. 2026-07-26 14:54 UTCEPSS rescore
  19. 2026-07-26 14:54 UTCEPSS rescore
  20. 2026-07-26 14:29 UTCEG score recompute
  21. 2026-07-26 14:29 UTCGHSA enrichment
  22. 2026-07-26 02:56 UTCEG score recompute
  23. 2026-07-26 02:55 UTCGHSA enrichment
  24. 2026-07-25 14:18 UTCEPSS rescore
  25. 2026-07-25 14:18 UTCEPSS rescore
Show 2 more
  1. 2026-07-24 16:53 UTCEG score recompute
  2. 2026-07-24 16:52 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-66035?
CVE-2026-66035 is a high vulnerability published on July 24, 2026. libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packetlength smaller than the cipher's block size during Encrypt-then-MAC…
When was CVE-2026-66035 disclosed?
CVE-2026-66035 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-2026-66035 actively exploited?
CVE-2026-66035 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 75.6% of all scored CVEs.
What is the CVSS score of CVE-2026-66035?
CVE-2026-66035 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-66035?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-66035, 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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