Critical severity · published Feb 24, 2026
CVE-2026-2776
Sandbox escape due to incorrect boundary conditions in the Telemetry component in External Software
10.0
CVSS
0.6%
EPSS
No
On KEV
Description
Sandbox escape due to incorrect boundary conditions in the Telemetry component in External Software. This vulnerability was fixed in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 47% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FI
Firefox · Mozilla
before 115.33.0; before 148.0; 128.0 before 140.8.0 · source: NVD
TH
Thunderbird · Mozilla
before 140.8.0; before 148.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-2776
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-2776
Issue Tracking
https://bugzilla.mozilla.org/show_bug.cgi?id=2015266
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-13/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-14/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-15/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-16/
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-17/
More from Firefox
10.0
CVE-2019-11708
Mozilla Firefox and Thunderbird Sandbox Escape Vulnerability
9.8
CVE-2024-9680
Mozilla Firefox Use-After-Free Vulnerability
9.8
CVE-2010-3765
Mozilla Multiple Products Remote Code Execution Vulnerability
9.6
CVE-2022-26486
Mozilla Firefox Use-After-Free Vulnerability
8.8
CVE-2023-5217
Google Chromium libvpx Heap Buffer Overflow Vulnerability