CVE-2026-74959: Mozilla Firefox vulnerability (CVSS 9.1)

Description

Mitigation bypass in the Storage: Cache API component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

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

Affected products

Mozilla Firefox≥ 141.0 < 153.1.0 · < 140.14.0

Mozilla Thunderbird≥ 141.0 < 153.1.0 · < 140.14.0

Remediation

Fixed in

Mozilla Firefox≥ 153.1.0

Mozilla Thunderbird≥ 153.1.0

Patch & vendor advisories

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2047853Permissions Required
https://www.mozilla.org/security/advisories/mfsa2026-74/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-76/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-77/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-78/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-79/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-80/Vendor Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-74959 being actively exploited?

CVE-2026-74959 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.48%.

How severe is CVE-2026-74959?

CVE-2026-74959 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.48% probability of exploitation.

Which products are affected by CVE-2026-74959?

Affected products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-74959?

Upgrade affected software to a fixed version, for example Mozilla Firefox 153.1.0, Mozilla Thunderbird 153.1.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-74959 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.

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