Description

Use-after-free in the Networking: HTTP component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

EPSS — Exploit Prediction

0.0038

Probability of exploitation

0.30%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

References

Other References

https://bugzilla.mozilla.org/show_bug.cgi?id=2036929 https://www.mozilla.org/security/advisories/mfsa2026-57/ https://www.mozilla.org/security/advisories/mfsa2026-58/ https://www.mozilla.org/security/advisories/mfsa2026-59/ https://www.mozilla.org/security/advisories/mfsa2026-60/ https://www.mozilla.org/security/advisories/mfsa2026-61/

Frequently Asked Questions

What is CVE-2026-12291? +

Use-after-free in the Networking: HTTP component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

How do I check if I'm vulnerable to CVE-2026-12291? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.