Heap-based Buffer Overflow The advisory has been revoked - it doesn't affect any version of package libssh2 (opens in a new tab)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-DEBIAN12-LIBSSH2-18300253
- published25 Jul 2026
- disclosed24 Jul 2026
Introduced: 24 Jul 2026
CVE-2026-66035 (opens in a new tab)Amendment
The Debian security team deemed this advisory irrelevant for Debian:12.
NVD Description
Note: Versions mentioned in the description apply only to the upstream libssh2 package and not the libssh2 package as distributed by Debian.
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.