CVE-2021-29991
High
Published: 03 November 2021
Published
03 November 2021
Modified
21 November 2024
KEV Added
—
Patch
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CVSS Score v3.1
8.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
EPSS Score
0.0031
54.3th percentile
Risk Priority
16
60% EPSS · 20% KEV · 20% CVSS
Summary
CVE-2021-29991 is a high-severity HTTP Request/Response Smuggling (CWE-444) vulnerability in Mozilla Firefox. Its CVSS base score is 8.1 (High).
Operationally, ranked in the top 45.7% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2021-16450
Vulnerability details
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.
- CWE(s)
Related Threats
No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.
Affected Assets
mozilla
firefox
≤ 91.0.1
mozilla
thunderbird
≤ 91.0.1
Mitigating Controls
No mitigating controls mapped yet. The per-CVE control annotator has not reached this CVE.