What is CVE-2025-1020?

CVE-2025-1020 is a critical-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2025-02-04.

How severe is CVE-2025-1020?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Mozilla Firefox

CVE-2025-1020

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 fixed in Firefox 135 and Thunderbird 135.

Vulnerability class: Buffer Overflow

EPSS: 0.005 (41.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Affected products

Mozilla Firefox — versions 135
Mozilla Thunderbird — versions 135

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

security@mozilla.org (Broken Link)
security@mozilla.org (Vendor Advisory)
security@mozilla.org (Vendor Advisory)

Frequently asked questions

What is CVE-2025-1020?: CVE-2025-1020 is a critical-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2025-02-04.
How severe is CVE-2025-1020?: Critical severity. CVSS v3 base score is 9.8 out of 10.