CVE-2025-1009: Mozilla Firefox use-after-free (CVSS 9.8)

Description

An attacker could have caused a use-after-free via crafted XSLT data, leading to a potentially exploitable crash. This vulnerability was fixed in Firefox 135, Firefox ESR 115.20, Firefox ESR 128.7, Thunderbird 128.7, and Thunderbird 135.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Mozilla Firefox< 135.0 · ≥ 128.1.0 < 128.7.0 · < 115.20.0

Mozilla Thunderbird≥ 131.0 < 135.0 · ≥ 128.0.1 < 128.7.0

Remediation

Fixed in

Mozilla Firefox≥ 135.0

Mozilla Thunderbird≥ 135.0

Patch & vendor advisories

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1936613Permissions Required
https://lists.debian.org/debian-lts-announce/2025/02/msg00005.html
https://lists.debian.org/debian-lts-announce/2025/02/msg00006.html
https://www.mozilla.org/security/advisories/mfsa2025-07/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-08/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-09/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-10/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-11/Vendor Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2025-1009 being actively exploited?

CVE-2025-1009 is not in the CISA KEV catalog. Its EPSS exploit probability is 1.21%.

How severe is CVE-2025-1009?

CVE-2025-1009 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 1.21% probability of exploitation.

Which products are affected by CVE-2025-1009?

Affected products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2025-1009?

Upgrade affected software to a fixed version, for example Mozilla Firefox 135.0, Mozilla Thunderbird 135.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2025-1009 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation works Book a demo