How severe is CVE-2025-1009?

CVE-2025-1009 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2025-1009 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (64th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-1009?

CVE-2025-1009 primarily affects Mozilla Firefox. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2025-1009?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2025-1009 have an EU (EUVD) identifier?

Yes. CVE-2025-1009 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-1964.

When was CVE-2025-1009 published?

CVE-2025-1009 was published on 2025-02-04 and last updated on 2026-06-17.

CVE-2025-1009

CVE-2025-1009 is a critical-severity vulnerability in Mozilla Firefox with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-416.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 1% (64th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-1964
Weakness: CWE-416
Affected product: Mozilla Firefox
Published: 2025-02-04
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2025-1009?: 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.
How severe is CVE-2025-1009?: CVE-2025-1009 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2025-1009 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (64th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-1009?: CVE-2025-1009 primarily affects Mozilla Firefox. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2025-1009?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2025-1009 have an EU (EUVD) identifier?: Yes. CVE-2025-1009 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-1964.
When was CVE-2025-1009 published?: CVE-2025-1009 was published on 2025-02-04 and last updated on 2026-06-17.

References

Affected products (4)

cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:-:*:*:*

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Other CWE-416 (Use After Free) vulnerabilities

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CVE-2026-4688 — Critical (CVSS 10.0): Sandbox escape due to use-after-free in the Disability Access APIs component. This vulnerability was fixed in Firefox…
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CVE-2024-43102 — Critical (CVSS 10.0): Concurrent removals of certain anonymous shared memory mappings by using the UMTX_SHM_DESTROY sub-request of…
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