CVE-2026-5734Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1.
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No exploitation reported and no EPSS estimate yet.
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Memory safety bugs present in Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.
- CVSS
- 9.8 CRITICAL (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- CWE-787, CWE-120
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Modified
- Record last updated
- Jul 15, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
mozilla firefox mozilla:firefox | before 140.9.1; before 149.0.2 | NVD |
mozilla thunderbird mozilla:thunderbird | before 140.9.1; before 149.0.2 | NVD |
References
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=2022369%2C2023026%2C2023545%2C2023555%2C2023958%2C2025422%2C2025468%2C2025492%2C2025505broken-link, issue-tracking
- https://www.mozilla.org/security/advisories/mfsa2026-25/vendor-advisory
- https://www.mozilla.org/security/advisories/mfsa2026-27/vendor-advisory
- https://www.mozilla.org/security/advisories/mfsa2026-28/
- https://www.mozilla.org/security/advisories/mfsa2026-29/
- https://access.redhat.com/errata/RHSA-2026:11805
- https://access.redhat.com/errata/RHSA-2026:11813
- https://access.redhat.com/errata/RHSA-2026:12264
- https://access.redhat.com/errata/RHSA-2026:13342
- https://access.redhat.com/errata/RHSA-2026:13412
- https://access.redhat.com/errata/RHSA-2026:13533
- https://access.redhat.com/errata/RHSA-2026:13582
- https://access.redhat.com/errata/RHSA-2026:13583
- https://access.redhat.com/errata/RHSA-2026:13596
- https://access.redhat.com/errata/RHSA-2026:13600
- https://access.redhat.com/errata/RHSA-2026:13665
- https://access.redhat.com/errata/RHSA-2026:13682
- https://access.redhat.com/errata/RHSA-2026:13683
- https://access.redhat.com/errata/RHSA-2026:13922
- https://access.redhat.com/errata/RHSA-2026:13977
- https://access.redhat.com/errata/RHSA-2026:14223
- https://access.redhat.com/errata/RHSA-2026:14303
- https://access.redhat.com/errata/RHSA-2026:15889
- https://access.redhat.com/errata/RHSA-2026:7671
- https://access.redhat.com/errata/RHSA-2026:7672
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.