CVE-2025-1020
Published: 04 February 2025
Summary
CVE-2025-1020 is a critical-severity Out-of-bounds Write (CWE-787) vulnerability in Mozilla Firefox. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked in the top 30.8% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-16 (Memory Protection) and SI-2 (Flaw Remediation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly mandates timely remediation of flaws like CVE-2025-1020 memory safety bugs by applying patches such as upgrading to Firefox 135 and Thunderbird 135.
Implements memory protection mechanisms like ASLR and DEP to minimize exploitation of memory corruption bugs such as out-of-bounds writes in CVE-2025-1020.
Enables vulnerability scanning to identify systems running vulnerable Firefox 134 or Thunderbird 134 affected by CVE-2025-1020.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Memory corruption (out-of-bounds write) directly enables remote arbitrary code execution in a client application (browser/email client) with no user interaction required.
NVD Description
Memory safety bugs present in Firefox 134 and Thunderbird 134. 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…
more
fixed in Firefox 135 and Thunderbird 135.
Deeper analysisAI
CVE-2025-1020 is a set of memory safety bugs (classified under CWE-787: Out-of-bounds Write) affecting Firefox version 134 and Thunderbird version 134. These bugs exhibited evidence of memory corruption, which Mozilla presumes could be exploited with sufficient effort to achieve arbitrary code execution. The vulnerability carries a CVSS v3.1 base score of 9.8, reflecting its critical severity.
The vulnerability is exploitable remotely over the network (AV:N) with low attack complexity (AC:L), requiring no privileges (PR:N) or user interaction (UI:N), and without changing scope (S:U). An attacker could leverage it to gain high-impact access to confidentiality (C:H), integrity (I:H), and availability (A:H), potentially fully compromising affected browsers or email clients.
Mozilla's security advisories (MFSA 2025-07 and MFSA 2025-11) detail the fixes applied in Firefox 135 and Thunderbird 135, recommending immediate upgrades to these patched versions. Additional technical details are available in the associated Bugzilla entries for bugs 1939063 and 1942169.
Details
- CWE(s)