CVE-2026-66034 — libssh2 Heap Out-of-Bounds Read via publickey subsystem

Affected: libssh2

libssh2 through 1.11.1, fixed in commit a13bb6c, contains a missing bounds check vulnerability that allows a malicious SSH server to trigger an arbitrary-length heap out-of-bounds read and a free of an uninitialized pointer via the publickey subsystem. In libssh2_publickey_list_fetch(), the version 1 response parser reads a server-controlled comment_len value and advances the parse pointer without verifying sufficient bytes remain in the buffer, causing the out-of-bounds read to leak heap pointers from adjacent allocations defeating ASLR, followed by heap allocator state corruption when the error cleanup path frees an uninitialized pointer from a non-zeroed realloc() region.

USN-8799-1 — libssh2 vulnerabilities

Affected: Ubuntu:Pro:14.04:LTS: libssh2, Ubuntu:Pro:16.04:LTS: libssh2, Ubuntu:Pro:18.04:LTS: libssh2, Ubuntu:Pro:20.04:LTS: libssh2, Ubuntu:22.04:LTS: libssh2

It was discovered that libssh2 incorrectly handled certain publickey subsystem attributes. A remote attacker controlling a malicious SSH server could use this issue to cause a denial of service or possibly execute arbitrary code. (CVE-2026-58050)

It was discovered that libssh2 did not properly initialize publickey list entries before parsing. A remote attacker controlling a malicious SSH server could use this issue to cause a denial of service or possibly execute arbitrary code. (CVE-2026-58051)

It was discovered that libssh2 incorrectly handled certain SFTP server responses. A remote attacker controlling an SSH server could use this issue to cause libssh2 to crash or possibly execute arbitrary code. (CVE-2026-66032)

It was discovered that libssh2 did not properly check bounds in certain publickey subsystem responses. A remote attacker controlling a malicious SSH server could use this issue to cause a denial of service or possibly execute arbitrary code.. (CVE-2026-66034)

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CVE-2026-66034 — libssh2 Heap Out-of-Bounds Read via publickey subsystem

USN-8799-1 — libssh2 vulnerabilities