# CVE-2019-25634: Base64 Decoder 1.1.2 Local Buffer Overflow SEH Egghunter

> Local attackers can execute arbitrary code via a stack-based buffer overflow in Base64 Decoder by crafting a malicious input file.

- **Severity:** High 8.6 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Mar 2026
- **Updated:** 15 Jul 2026
- **Also known as:** GHSA-cpr2-5chx-jmj3

## What is CVE-2019-25634?

CVE-2019-25634 is a high-severity memory corruption vulnerability in 4Mhz Base64 Decoder, published on 24 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Base64 Decoder 1.1.2 contains a stack-based buffer overflow vulnerability that allows local attackers to execute arbitrary code by triggering a structured exception handler (SEH) overwrite. Attackers can craft a malicious input file that overflows a buffer, overwrites the SEH chain with a POP-POP-RET gadget address, and uses an egghunter payload to locate and execute shellcode for code execution.

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

## Which versions are affected by CVE-2019-25634?

It affects 1 product.


Products: 4mhz Base64 Decoder.

## How do I fix CVE-2019-25634?

No fix has been published for CVE-2019-25634 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-25634 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-25634 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-25634 and fix it if it is affected.

What it is: CVE-2019-25634 is a high-severity memory corruption vulnerability in 4Mhz Base64 Decoder, published on 24 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2019-25634 exists.

Affected product: 4Mhz Base64 Decoder. 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-2019-25634/ (Markdown: https://insights.sbomify.com/CVE-2019-25634/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-25634
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-25634
- OSV: https://osv.dev/vulnerability/CVE-2019-25634

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From sbomify Insights: https://insights.sbomify.com/CVE-2019-25634/
Summaries are generated and may contain mistakes; the official description above is the record.