Medium [CVE-2026-58051] Denial of service or information disclosure via malformed SSH publickey response

libssh2 through 1.11.1 grows its publickey list with SSH2_REALLOC but does not zero-initialize new entries before parsing populates them, so a parse failure reaching the cleanup path leaves libssh2_publickey_list_free operating on an uninitialized entry.

A malicious SSH server offering the publickey subsystem can use a malformed response to make cleanup free an uninitialized, attacker-influenceable attrs pointer in a connecting libssh2 client. A flaw in libssh2 allows a malicious SSH server to send a malformed public key response, triggering an invalid memory cleanup.

This can cause the connecting client application to crash or leak information. Moderate: This flaw in libssh2 can lead to a denial of service or information disclosure in client applications when connecting to a malicious SSH server.

The vulnerability arises from improper handling of uninitialized memory during public key list processing, which an attacker can trigger with a specially crafted response. Exploitation requires active interaction with a compromised or malicious server, limiting the attack surface to untrusted connections.

Note: Red Hat Enterprise Linux (RHEL) 8 and newer are not affected by this flaw, as they do not ship the libssh2 package. Red Hat severity: Moderate — CVSS 6.5 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H).

Weakness: CWE-824.