# CVE-2025-0240: Compartment mismatch when parsing JavaScript JSON module

> A use-after-free vulnerability in Firefox and Thunderbird allows attackers to execute arbitrary code via crafted JavaScript JSON modules.

- **Severity:** Medium 4.0 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Jan 2025
- **Updated:** 13 Apr 2026
- **Also known as:** DEBIAN-CVE-2025-0240, GHSA-f3xq-g93v-w8cv, UBUNTU-CVE-2025-0240

## What is CVE-2025-0240?

CVE-2025-0240 is a medium-severity use after free vulnerability in Mozilla Firefox, published on 7 Jan 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Parsing a JavaScript module as JSON could, under some circumstances, cause cross-compartment access, which may result in a use-after-free. This vulnerability was fixed in Firefox 134, Firefox ESR 128.6, Thunderbird 134, and Thunderbird 128.6.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-0240?

It affects 2 products.


Products: Mozilla Firefox, Mozilla Thunderbird.

## How do I fix CVE-2025-0240?

Upgrade to a fixed version.

## Is CVE-2025-0240 being exploited?

There is no known exploitation of CVE-2025-0240 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-2025-0240 and fix it if it is affected.

What it is: CVE-2025-0240 is a medium-severity use after free vulnerability in Mozilla Firefox, published on 7 Jan 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-2025-0240 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-2025-0240/ (Markdown: https://insights.sbomify.com/CVE-2025-0240/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-0240
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-0240
- OSV: https://osv.dev/vulnerability/CVE-2025-0240

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-0240/
Summaries are generated and may contain mistakes; the official description above is the record.