Mozilla Firefox
CVE-2026-84145
Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of these bugs showed evidence of memory corruption or another security-relevant defect and we presume that with enough effort some of these could have been exploited. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
What this means for your business
- It affects Mozilla Firefox. It matters if your company, or a supplier that handles your data, runs it.
- An attacker can use it remotely, over a network, without a login, but only after tricking someone into an action such as opening a file or a link.
- FIRST's prediction model gives it a 0.4% chance of attack attempts being seen in the next 30 days, ranking above 30% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Mozilla Firefox, and which version. The affected versions are listed further down this page.
- 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
Fastnexa security experts
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Scoring
- CVSS
- 7.5 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H- Weakness
- CWE-119
- Assigned by
- security@mozilla.org
Dates
- Published
- 2026-09-01
- Last modified
- 2026-09-03
- Sources
- NVD
Affected products
- Mozilla Firefox- 115.40.0, 116.0 - 140.15.0, 141.0.0 - 153.2.0, 154.0.0 - 155.0.0
- Mozilla Thunderbird- 140.15.0, 141.0 - 153.2.0, 154.0 - 155.0
As listed in the NVD configuration data. Not a statement about your estate.
References
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=2054640%2C2054650%2C2054652%2C2055693%2C2055705%2C2058051%2C2058652%2C2058660%2C2059027%2C2061220%2C2061242%2C2061285%2C2061300%2C2061316%2C2061397
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=2058001%2C2059139%2C2062400%2C2062419
- https://bugzilla.mozilla.org/show_bug.cgi?id=2055678
- https://www.mozilla.org/security/advisories/mfsa2026-82/
- https://www.mozilla.org/security/advisories/mfsa2026-83/
- https://www.mozilla.org/security/advisories/mfsa2026-84/
- https://www.mozilla.org/security/advisories/mfsa2026-85/
- https://www.mozilla.org/security/advisories/mfsa2026-86/
- https://www.mozilla.org/security/advisories/mfsa2026-87/
- https://www.mozilla.org/security/advisories/mfsa2026-88/