The vulnerability CVE-2025-4877 in libssh occurs specifically in 32-bit builds when the ssh_get_fingerprint_hash() function receives an unexpectedly large input buffer. This triggers an integer overflow in the bin_to_base64() function, causing memory under allocation and enabling out-of-bounds writes that corrupt the heap. The issue has been assigned a CVSS 3.1 base score of 4.5 (medium severity) with attack vector local, high attack complexity, low privileges required, no user interaction, and impacts confidentiality, integrity, and availability to a limited extent. Red Hat has published advisories and released patches for libssh in Red Hat Enterprise Linux 9 and related variants to fix this vulnerability.

Successful exploitation can lead to heap corruption due to out-of-bounds writes, potentially causing application instability or crashes. The impact on confidentiality, integrity, and availability is rated low to medium. The vulnerability requires local access with high complexity and low privileges, limiting the ease of exploitation. It affects only 32-bit builds of libssh.

Red Hat has released official security updates that fix this vulnerability in libssh packages for Red Hat Enterprise Linux 9 and related distributions. Users should apply these updates promptly to remediate the issue. Refer to Red Hat advisory RHSA-2026:18683 and the linked update instructions at https://access.redhat.com/articles/11258 for detailed patching guidance. No additional mitigation is required beyond applying the official fix.