CVE-2026-109740 Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component
Critical 9.6
Published
Updated
Check this codebase for CVE-2026-109740 and fix it if it is affected.
What it is: CVE-2026-109740 is a critical vulnerability in Mozilla Firefox, published on 13 Oct 2026.
Exploitation: There is no known exploitation of CVE-2026-109740 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-2026-109740/ (Markdown: https://insights.sbomify.com/CVE-2026-109740/index.md)
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-109740?
CVE-2026-109740 is a critical vulnerability in Mozilla Firefox, published on 13 Oct 2026.
Official description
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, and Thunderbird 153.5.
Weakness: CWE-119
Which versions are affected by CVE-2026-109740?
How do I fix CVE-2026-109740?
Upgrade to a fixed version.
Is CVE-2026-109740 being exploited?
There is no known exploitation of CVE-2026-109740 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-109740, GHSA-rp57-hr33-wfgr, UBUNTU-CVE-2026-109740.