Mozilla Multiple Products Remote Code Execution Vulnerability

CheckOps priority index

8.8/10 Patch within 24 h

Severity9.8

Probability8.3

Exploitation4/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 83.2% higher than 99.7% of CVEs

CVSS 3.1 9.8 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:

Exploited for 393 days 06 Oct 2025

CISA due date 27 Oct 2025 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 4 / 5

KEV catalog (CISA)06 Oct 2025
Exploited in EUVD (ENISA)06 Oct 2025
Used by ransomwareno
EPSS above 10 %83.2%
No account, over the networkyes

What to do

Fix

Apply the vendor’s fix as soon as it is available.

CISA guidance: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Description ENISA EUVD

Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x before 2.0.10, when JavaScript is enabled, allows remote attackers to execute arbitrary code via vectors related to nsCSSFrameConstructor::ContentAppended, the appendChild method, incorrect index tracking, and the creation of multiple frames, which triggers memory corruption, as exploited in the wild in October 2010 by the Belmoo malware.

Affected products

Multiple Products

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

27 Oct 2010
Published
06 Oct 2025
Exploitation reported (ENISA)
06 Oct 2025
Added to the KEV catalog
27 Oct 2025
CISA remediation due date
26 Sept 2026
EPSS peak: 83.2%

Other exploited vulnerabilities from the same vendor

CVE-2024-9680Mozilla Firefox Use-After-Free Vulnerability
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CVE-2016-9079Mozilla Firefox, Firefox ESR, and Thunderbird Use-After-Free Vulnerability
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CVE-2015-4495Mozilla Firefox Security Feature Bypass Vulnerability
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CVE-2019-11708Mozilla Firefox and Thunderbird Sandbox Escape Vulnerability
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CVE-2019-11707Mozilla Firefox and Thunderbird Type Confusion Vulnerability
7.1 · Background exploitation
CVE-2013-1690Mozilla Firefox and Thunderbird Denial-of-Service Vulnerability
8.0 · Background exploitation