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

> An integer overflow in libssh's base64 conversion can cause heap corruption and potential code execution on 32-bit systems.

- **Severity:** Medium 4.5 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Aug 2025
- **Updated:** 31 Aug 2026
- **Also known as:** BELL-CVE-2025-4877, DEBIAN-CVE-2025-4877, GHSA-pwrf-jm93-99r3, UBUNTU-CVE-2025-4877

## What is CVE-2025-4877?

CVE-2025-4877 is a medium-severity vulnerability in Red Hat Enterprise Linux 10, published on 20 Aug 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2025-4877?


## How do I fix CVE-2025-4877?

Apply the vendor's patch.

## Is CVE-2025-4877 being exploited?

There is no known exploitation of CVE-2025-4877 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-4877 and fix it if it is affected.

What it is: CVE-2025-4877 is a medium-severity vulnerability in Red Hat Enterprise Linux 10, published on 20 Aug 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-4877 in the wild and no public exploit code.

Affected product: Red Hat Enterprise Linux 10. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-4877/ (Markdown: https://insights.sbomify.com/CVE-2025-4877/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-4877
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-4877
- OSV: https://osv.dev/vulnerability/CVE-2025-4877

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-4877/
Summaries are generated and may contain mistakes; the official description above is the record.