CVE-2026-4700 Mitigation bypass in the Networking: HTTP component
Critical 9.8
Published
Updated
Check this codebase for CVE-2026-4700 and fix it if it is affected.
What it is: CVE-2026-4700 is a critical vulnerability in Mozilla Firefox, published on 24 Mar 2026. 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-2026-4700 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-2026-4700/ (Markdown: https://insights.sbomify.com/CVE-2026-4700/index.md)
Attackers can bypass HTTP networking mitigations in Firefox and Thunderbird, requiring users to upgrade to patched versions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-4700?
CVE-2026-4700 is a critical vulnerability in Mozilla Firefox, published on 24 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Mitigation bypass in the Networking: HTTP component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Which versions are affected by CVE-2026-4700?
It affects 1 product.
Products include Mozilla Firefox.
How do I fix CVE-2026-4700?
Upgrade to a fixed version.
Is CVE-2026-4700 being exploited?
There is no known exploitation of CVE-2026-4700 in the wild and no public exploit code.
Other vulnerabilities in Mozilla Firefox
Sources
Also known as DEBIAN-CVE-2026-4700, GHSA-4pf4-jp4v-4g5c, UBUNTU-CVE-2026-4700.