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CVE-2026-8950

Mozilla Firefox vulnerability

9.3 CRITICALEPSS 0.21%
  1. Published19 May 2026

Description

Same-origin policy bypass in the Networking: HTTP component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionRequired
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

Affected products

Mozilla Firefox< 151.0.0 · < 140.11.0
Mozilla Thunderbird< 151.0.0 · < 140.11

Remediation

Fixed in
Mozilla Firefox≥ 151.0.0
Mozilla Thunderbird≥ 151.0.0

References

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Frequently asked

Is CVE-2026-8950 being actively exploited?

CVE-2026-8950 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.21%.

How severe is CVE-2026-8950?

CVE-2026-8950 has a CVSS 3.1 base score of 9.3, rated critical. EPSS estimates a 0.21% probability of exploitation.

Which products are affected by CVE-2026-8950?

Affected products include Mozilla Firefox, Mozilla Thunderbird.

How do I fix CVE-2026-8950?

Upgrade affected software to a fixed version, for example Mozilla Firefox 151.0.0, Mozilla Thunderbird 151.0.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-8950 against the real software inventory on every managed device, every day. 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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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.