CVE-2021-4126 - CVE House
Back to Database
Status published Unknown CVE-2021-4126

When receiving an OpenPGP/MIME signed email message that contains an...

Vulnerability Description

When receiving an OpenPGP/MIME signed email message that contains an additional outer MIME message layer, for example a message footer added by a mailing list gateway, Thunderbird only considered the inner signed message for the signature validity. This gave the false impression that the additional contents were also covered by the digital signature. Starting with Thunderbird version 91.4.1, only the signature that belongs to the top level MIME part will be considered for the displayed status. This vulnerability affects Thunderbird < 91.4.1.

Impact Analysis

Refer to official advisory for detailed impact metrics.

Remediation

Ensure systems are updated to the latest vendor-supplied patch levels.

THREAT MONITOR

Am I Vulnerable?

Launch our assessment wizard to check if your infrastructure is exposed to • CVE-2021-4126

Credits & Attribution

No credits recorded in the NVD database.

References

More from Mozilla

View All →
CVE-2025-9187
Memory safety bugs fixed in Firefox 142 and Thunderbird 142
Unknown 0
CVE-2025-9186
Spoofing issue in the Address Bar component of Firefox Focus for Android
Unknown 0
CVE-2025-9185
Memory safety bugs fixed in Firefox ESR 115.27, Firefox ESR 128.14, Thunderbird ESR 128.14, Firefox ESR 140.2, Thunderbird ESR 140.2, Firefox 142 and Thunderbird 142
Unknown 0
CVE-2025-9184
Memory safety bugs fixed in Firefox ESR 140.2, Thunderbird ESR 140.2, Firefox 142 and Thunderbird 142
Unknown 0
CVE-2025-9183
Spoofing issue in the Address Bar component
Unknown 0

Affected Vendor

Affected Software

Thunderbird
Vulnerable Versions:
unspecified

Timeline

Official Publish: December 22nd, 2022
Last Modified: April 16th, 2025
Added to House: July 21st, 2026

CVSS Vectors

No vector data available

Weaknesses (CWE)

No CWE data available

MITRE ATT&CK TTPs

No associated TTPs found for this vulnerability.