# CVE-2025-1936: Adding %00 and a fake extension to a jar: URL changed the interpretation of the contents

> Attackers can hide malicious code in jar URLs by using null bytes and fake extensions, bypassing content type checks in Firefox and Thunderbird.

- **Severity:** High 7.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Mar 2025
- **Updated:** 13 Apr 2026
- **Also known as:** DEBIAN-CVE-2025-1936, GHSA-x4j2-c46q-7jp5, UBUNTU-CVE-2025-1936

## What is CVE-2025-1936?

CVE-2025-1936 is a high-severity vulnerability in Mozilla Firefox, published on 4 Mar 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

jar: URLs retrieve local file content packaged in a ZIP archive. The null and everything after it was ignored when retrieving the content from the archive, but the fake extension after the null was used to determine the type of content. This could have been used to hide code in a web extension disguised as something else like an image. This vulnerability was fixed in Firefox 136, Firefox ESR 128.8, Thunderbird 136, and Thunderbird 128.8.

Weakness: CWE-158 (Improper Neutralization of Null Byte or NUL Character)

## Which versions are affected by CVE-2025-1936?

It affects 2 products.


Products: Mozilla Firefox, Mozilla Thunderbird.

## How do I fix CVE-2025-1936?

Upgrade to a fixed version.

## Is CVE-2025-1936 being exploited?

There is no known exploitation of CVE-2025-1936 in the wild and no public exploit code.

## Other vulnerabilities in Mozilla Firefox

- [CVE-2019-11708](https://insights.sbomify.com/CVE-2019-11708/): Mozilla Firefox and Thunderbird Sandbox Escape (critical 10.0, exploited in the wild)
- [CVE-2010-3765](https://insights.sbomify.com/CVE-2010-3765/): Mozilla Multiple Products Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2022-26486](https://insights.sbomify.com/CVE-2022-26486/): Mozilla Firefox Use-After-Free (critical 9.6, exploited in the wild)
- [CVE-2022-26485](https://insights.sbomify.com/CVE-2022-26485/): Mozilla Firefox Use-After-Free (high 8.8, exploited in the wild)
- [CVE-2019-11707](https://insights.sbomify.com/CVE-2019-11707/): Mozilla Firefox and Thunderbird Type Confusion (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-1936 and fix it if it is affected.

What it is: CVE-2025-1936 is a high-severity vulnerability in Mozilla Firefox, published on 4 Mar 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-1936 in the wild and no public exploit code.

Affected product: Mozilla Firefox. 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-2025-1936/ (Markdown: https://insights.sbomify.com/CVE-2025-1936/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-1936
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-1936
- OSV: https://osv.dev/vulnerability/CVE-2025-1936

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-1936/
Summaries are generated and may contain mistakes; the official description above is the record.