Critical severity · published Apr 7, 2026
CVE-2026-5735
Memory safety bugs fixed in Firefox 149.0.2 and Thunderbird 149.0.2
9.8
CVSS
0.3%
EPSS
No
On KEV
Description
Memory safety bugs present in 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 and Thunderbird 149.0.2.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 17% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FI
Firefox · Mozilla
before 149.0.2 · source: NVD
TH
Thunderbird · Mozilla
before 149.0.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-5735
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-5735
Broken Link
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2025475%2C2025477
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-25/
www.mozilla.org
https://www.mozilla.org/security/advisories/mfsa2026-28/
access.redhat.com
https://access.redhat.com/security/cve/CVE-2026-5735
bugzilla.redhat.com
https://bugzilla.redhat.com/show_bug.cgi?id=2455904
security.access.redhat.com
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5735.json
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