What’s Vulnerable › Vulnerabilities

CVE-2021-29946

• Severity: high (CVSS 8.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-06-24 · updated 2026-06-17
• Weakness: CWE-190

Description

Ports that were written as an integer overflow above the bounds of a 16-bit integer could have bypassed port blocking restrictions when used in the Alt-Svc header. This vulnerability affects Firefox ESR < 78.10, Thunderbird < 78.10, and Firefox < 88.

Affected products

• Mozilla Firefox: before 88.0 — fixed in 88.0
• Mozilla Firefox ESR: before 78.10 — fixed in 78.10
• Mozilla Thunderbird: before 78.10 — fixed in 78.10

How to fix

Upgrade to a fixed version: Mozilla Firefox 88.0; Mozilla Firefox ESR 78.10; Mozilla Thunderbird 78.10. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1698503
• https://www.mozilla.org/security/advisories/mfsa2021-14/
• https://www.mozilla.org/security/advisories/mfsa2021-15/
• https://www.mozilla.org/security/advisories/mfsa2021-16/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1698503
• https://www.mozilla.org/security/advisories/mfsa2021-14/
• https://www.mozilla.org/security/advisories/mfsa2021-15/
• https://www.mozilla.org/security/advisories/mfsa2021-16/

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