What’s Vulnerable › Vulnerabilities

CVE-2026-84138: Denial-of-service in the PDF Viewer component

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-01 · updated 2026-09-03
• Weakness: CWE-400

Description

Denial-of-service in the PDF Viewer component. This vulnerability was fixed in Firefox 155 and Thunderbird 155.

Affected products

• Mozilla Firefox: before 155.0.0 — fixed in 155.0.0
• Mozilla Thunderbird: before 155.0 — fixed in 155.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 155.0.0; Mozilla Thunderbird 155.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2056164
• https://www.mozilla.org/security/advisories/mfsa2026-82/
• https://www.mozilla.org/security/advisories/mfsa2026-86/

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