CVE-2026-100822: Spoofing issue in the Networking: HTTP component

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-29 · updated 2026-10-13
Weakness: CWE-451

Description

Spoofing issue in the Networking: HTTP component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox 157.

Affected products

Mozilla Firefox: before 153.4.0; from 154.0.0 before 157.0.0 — fixed in 153.4.0, 157.0.0
Mozilla Thunderbird: before 153.4.0; from 154.0 before 157.0 — fixed in 153.4.0, 157.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 153.4.0, 157.0.0; Mozilla Thunderbird 153.4.0, 157.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2051115
https://www.mozilla.org/security/advisories/mfsa2026-100/
https://www.mozilla.org/security/advisories/mfsa2026-101/
https://www.mozilla.org/security/advisories/mfsa2026-103/
https://www.mozilla.org/security/advisories/mfsa2026-97/

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