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.
CVE-2026-66035
HIGHPre-NVD 7.57.5—Trending — 4 sources updated this week
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
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
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- 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 computedSeverity75% × 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 25, 2026
Advisory Details (3)
Auto-updated Jul 24, 2026Upstream 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-negotiationgithub_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/2198github_commit
commit 42e33d81577e (libssh2/libssh2)
Fix landed in libssh2/libssh2 commit 42e33d81577e — awaiting tagged release
https://github.com/libssh2/libssh2/commit/42e33d81577ed4b95d4b4f6f845e5ee8efe5eeb4Vendor Advisories for CVE-2026-66035(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 12× in last 7d / 12× 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.
- 2026-07-27 02:01 UTCEG score recompute
- 2026-07-27 02:01 UTCGHSA enrichment
- 2026-07-26 14:54 UTCEPSS rescore
- 2026-07-26 14:54 UTCEPSS rescore
- 2026-07-26 14:29 UTCEG score recompute
- 2026-07-26 14:29 UTCGHSA enrichment
- 2026-07-26 02:56 UTCEG score recompute
- 2026-07-26 02:55 UTCGHSA enrichment
- 2026-07-25 14:18 UTCEPSS rescore
- 2026-07-25 14:18 UTCEPSS rescore
- 2026-07-24 16:53 UTCEG score recompute
- 2026-07-24 16:52 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Same CWE
10 shownCWE-122
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 25, 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 v4.0 base score of 7.5 (CNA self-assessment; NVD's own analysis pending).
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
Explore the affected products and dependency analysis for CVE-2026-66035
Is Your Infrastructure Affected by CVE-2026-66035?
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