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

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.

CVSS

7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Weakness (CWE)

CWE-125, CWE-908

Known exploited

Not in CISA's KEV catalog

EPSS (exploitation in the next 30 days)

Not loaded for this CVE

Assigned by

VulnCheck

NVD analysis

Analyzed

Record last updated

Jul 27, 2026

First seen by InfoSec Signals

Oct 9, 2026

The CVE record on cve.org · NVD's entry

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