CVE-2021-29991

HighCVSS 8.1/10Last modified Jun 17, 2026

Description

Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two separate headers. This allowed for a header splitting attack against servers using HTTP/3. This vulnerability affects Firefox < 91.0.1 and Thunderbird < 91.0.1.

Metrics

CVSS 3.1 8.1/10CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

Weakness enumeration

CWE-444

Affected software

No affected versions have been published.

Timeline

Published: Nov 3, 2021
Last modified: Jun 17, 2026
NVD status: Modified

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