CVE-2026-124877 Use-after-free in the Layout: Positioned component
High 8.8
Published
Updated
Check this codebase for CVE-2026-124877 and fix it if it is affected.
What it is: CVE-2026-124877 is a high-severity vulnerability in Mozilla Firefox, published on 10 Nov 2026.
Exploitation: There is no known exploitation of CVE-2026-124877 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-2026-124877/ (Markdown: https://insights.sbomify.com/CVE-2026-124877/index.md)
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-124877?
CVE-2026-124877 is a high-severity vulnerability in Mozilla Firefox, published on 10 Nov 2026.
Official description
Use-after-free in the Layout: Positioned component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, Firefox ESR 153.7, Thunderbird 160, and Thunderbird 153.7.
Weakness: CWE-416
Which versions are affected by CVE-2026-124877?
How do I fix CVE-2026-124877?
Upgrade to a fixed version.
Is CVE-2026-124877 being exploited?
There is no known exploitation of CVE-2026-124877 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-124877, GHSA-4grq-p5w6-v4j4, UBUNTU-CVE-2026-124877.