High [CVE-2026-58050] Heap buffer overflow via integer overflow in publickey attribute allocation

libssh2 through 1.11.1 reads an attacker-controlled 32-bit attribute count from a publickey-subsystem response and uses it in the allocation num_attrs * sizeof(libssh2_publickey_attribute) without bounds checking, so on 32-bit platforms the multiplication overflows to an undersized buffer.

A malicious SSH server can then drive the attribute-parsing loop to write past the allocation, causing a heap buffer overflow in a connecting libssh2 client. A flaw in libssh2 allows a malicious SSH server to trigger a memory overflow by sending a manipulated attribute count.

This can cause the connecting client to crash or allow unauthorized code execution. By manipulating the publickey-subsystem response, an attacker could cause an integer overflow, potentially leading to denial of service or arbitrary code execution on Red Hat systems using libssh2 to establish SSH 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 7 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H).

Weakness: CWE-787. Affected Red Hat products: Red Hat Hardened Images; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7.

Will not fix / out of support: Red Hat Enterprise Linux 6. Red Hat fixing advisory: RHSA-2026:54070.

Affected products named by the advisory: Red Hat package: libssh2.