CVE-2026-12291
Use-after-free in Firefox HTTP stack may lead to code execution or crash.
Is CVE-2026-12291 being exploited?
Not confirmed. CVE-2026-12291 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.38% probability of exploitation in the next 30 days.
How severe is CVE-2026-12291?
CVE-2026-12291 is rated High with a CVSS score of 8.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-12291?
Yes. A fix has been recorded for CVE-2026-12291. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-12291 affect?
CVE-2026-12291 affects Firefox (Desktop), Firefox ESR, Thunderbird. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-12291?
Update to 152+ (Firefox/Thunderbird).
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote code execution or crash via crafted HTTP requests in Firefox/Thunderbird.
Patch when possible