# CVE-2025-4877: Libssh: write beyond bounds in binary to base64 conversion functions

Status: published. Published: 2025-08-20. Updated: 2026-11-05.

There's a vulnerability in the libssh package where when a libssh consumer passes in an unexpectedly large input buffer to ssh_get_fingerprint_hash() function. In such cases the bin_to_base64() function can experience an integer overflow leading to a memory under allocation, when that happens it's possible that the program perform out of bounds write leading to a heap corruption.
This issue affects only 32-bits builds of libssh.

## Remediation

No remediation reported in collected sources

## Affected products and versions

-  /  (libssh): ≥ 0; < 0.11.2 (affected, semver). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (libssh): ≥ 0:0.10.4-18.el9; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10 (libssh): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (libssh2): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (libssh2): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (libssh): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 4.5 (medium); CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L; source: CNA: redhat

- CVSS 3.1: 4.5 (medium); CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L; source: NVD: secalert@redhat.com

- CISA KEV: No listing in collected sources

- EPSS: 0.20% as of 2026-11-05; percentile 10.32%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-787

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/errata/RHSA-2026:18683 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2025-4877 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2376193 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://git.libssh.org/projects/libssh.git/commit/?h=stable-0.11&id=6fd9cc8ce3958092a1aae11f1f2e911b2747732d (CNA: redhat)

- https://www.libssh.org/security/advisories/CVE-2025-4877.txt (CNA: redhat)

- https://access.redhat.com/errata/RHSA-2026:18683 (secalert@redhat.com)

- https://access.redhat.com/security/cve/CVE-2025-4877 (secalert@redhat.com)

- https://bugzilla.redhat.com/show_bug.cgi?id=2376193 (secalert@redhat.com)

- https://git.libssh.org/projects/libssh.git/commit/?h=stable-0.11&id=6fd9cc8ce3958092a1aae11f1f2e911b2747732d (secalert@redhat.com)

- https://www.libssh.org/security/advisories/CVE-2025-4877.txt (secalert@redhat.com)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2025-4877; retrieved 2026-11-05; source updated 2026-11-05

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-4877; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2025-4877; retrieved 2026-11-05; source updated Not reported

Revision: d8e63fadcedb9e6425995221ba2ca0a77c9cf709eded56fc129e4d3dd0527777

Canonical: https://y2.dev/cve/CVE-2025-4877

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