CVE-2026-118021 Sandbox escape due to use-after-free in the XPCOM component
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Published
Updated
Check this codebase for CVE-2026-118021 and fix it if it is affected.
What it is: CVE-2026-118021 is a vulnerability in Mozilla Firefox, published on 27 Oct 2026.
Exploitation: There is no known exploitation of CVE-2026-118021 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-2026-118021/ (Markdown: https://insights.sbomify.com/CVE-2026-118021/index.md)
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-118021?
CVE-2026-118021 is a vulnerability in Mozilla Firefox, published on 27 Oct 2026.
Official description
Sandbox escape due to use-after-free in the XPCOM component. This vulnerability was fixed in Firefox 159 and Thunderbird 159.
Which versions are affected by CVE-2026-118021?
How do I fix CVE-2026-118021?
No fix has been published for CVE-2026-118021 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-118021 being exploited?
There is no known exploitation of CVE-2026-118021 in the wild and no public exploit code.
Sources
Also known as GHSA-3hc8-89qm-6758, UBUNTU-CVE-2026-118021.