CVE-2026-12299
MEDIUM 5.4JIT miscompilation in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.
No known exploitation, public exploit, or elevated probability at this time. Track for changes.
Exploitation likelihood
0.3%chance of exploitation in 30 days · 23rd percentile
Impact if exploited
5.4CVSS 3.1 · MEDIUM
- ConfidentialityLow
- IntegrityLow
- AvailabilityNone
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ✓Privileges: No account or privileges required
- ⚠User interaction: A user must take an action (click / open a file)
- ✓Complexity: No special conditions — reliably repeatable
✓ lowers the bar for an attacker · ⚠ raises it
Proof of concept & exploit code
- github-search Search GitHub for public PoC repos
Test against your own equipment
curl -s https://vulnpedia.com/cve/CVE-2026-12299/poc.jsonMachine-readable PoC index for this CVE (for automation).Listed for defensive triage, patch verification, and authorized testing on systems you own. Machine-readable: /cve/CVE-2026-12299/poc.json
Affected
Products Firefox Thunderbird Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 10.0 Extended Update Support Red Hat Enterprise Linux 7 Extended Lifecycle Support Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support Red Hat Enterprise Linux 8.4 Extended Update Support Long Life Add On Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support Red Hat Enterprise Linux 8.6 Extended Update Support Long Life Add On Red Hat Enterprise Linux 8.8 Telecommunications Update Service Red Hat Enterprise Linux 8.8 Update Services For Sap Solutions
Weakness (CWE)
- CWE-843: Access of Resource Using Incompatible Type ('Type Confusion')
- CWE-733: Compiler Optimization Removal or Modification of Security-critical Code
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Known Affected Software Configurations
| Vendor | Product | Version range |
|---|---|---|
| Mozilla | Firefox | < 115.37.0 |
| Mozilla | Firefox | < 152.0 |
| Mozilla | Firefox | ≥ 140.0 and < 140.12.0 |
| Mozilla | Thunderbird | < 152.0.0 |
| Mozilla | Thunderbird | ≥ 140.0 and < 140.12.0 |
All CVSS metrics
- MEDIUM 5.4 v3.1 · ADP Primary
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N - HIGH 7.5 v3.1 · ADP Primary
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H - MEDIUM 5.4 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N - HIGH 7.5 v3.1 · NVD Secondary
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
References
Advisories
- 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/
- https://access.redhat.com/errata/RHSA-2026:38506
- https://access.redhat.com/errata/RHSA-2026:36100
- https://access.redhat.com/errata/RHSA-2026:38751
- https://access.redhat.com/errata/RHSA-2026:27733
- https://access.redhat.com/errata/RHSA-2026:30846
- https://access.redhat.com/errata/RHSA-2026:27717
- https://access.redhat.com/errata/RHSA-2026:33445
- https://access.redhat.com/errata/RHSA-2026:36102
- https://access.redhat.com/errata/RHSA-2026:39428
- https://access.redhat.com/errata/RHSA-2026:37210
- https://access.redhat.com/errata/RHSA-2026:39141
- https://access.redhat.com/errata/RHSA-2026:36103
- https://access.redhat.com/errata/RHSA-2026:39142
- https://access.redhat.com/errata/RHSA-2026:36101
- https://access.redhat.com/errata/RHSA-2026:39706
- https://access.redhat.com/errata/RHSA-2026:39011
- https://access.redhat.com/errata/RHSA-2026:38753
- https://access.redhat.com/errata/RHSA-2026:37391
- https://access.redhat.com/errata/RHSA-2026:38750
- https://access.redhat.com/errata/RHSA-2026:27734
- https://access.redhat.com/errata/RHSA-2026:29940