CVE-2026-66035 (GCVE-0-2026-66035)
Vulnerability from cvelistv5 – Published: 2026-07-24 16:45 – Updated: 2026-07-28 01:06 X_Open Source
VLAI
EPSS
VEX
Title
libssh2 Heap Buffer Overflow via ETM Cipher Negotiation
Summary
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.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-07-24 00:00 UTC
CWE
- CWE-122 - Heap-based Buffer Overflow
Assigner
References
3 references
| URL | Tags |
|---|---|
| https://github.com/libssh2/libssh2/pull/2198 | issue-trackingpatch |
| https://github.com/libssh2/libssh2/commit/42e33d8… | patch |
| https://www.vulncheck.com/advisories/libssh2-heap… | third-party-advisory |
Impacted products
Date Public
2026-07-03 00:00
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