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CVE-2021-29991

Date: November 2, 2021

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.

Severity Score

Related Resources (7)

https://people.canonical.com/~ubuntu-security/cve/CVE-2021-29991
https://access.redhat.com/security/cve/CVE-2021-29991
https://www.mozilla.org/security/advisories/mfsa2021-37/
https://security.alpinelinux.org/vuln/CVE-2021-29991
https://nvd.nist.gov/vuln/detail/CVE-2021-29991
https://bugzilla.mozilla.org/show_bug.cgi?id=1724896
https://www.mend.io/vulnerability-database/CVE-2021-29991

Severity Score

Weakness Type (CWE)

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

CWE-444

CVSS v3.1

Base Score:
Attack Vector (AV): NETWORK
Attack Complexity (AC): LOW
Privileges Required (PR): NONE
User Interaction (UI): REQUIRED
Scope (S): UNCHANGED
Confidentiality (C): HIGH
Integrity (I): HIGH
Availability (A): NONE

CVSS v2

Base Score:
Access Vector (AV): NETWORK
Access Complexity (AC): MEDIUM
Authentication (AU): NONE
Confidentiality (C): PARTIAL
Integrity (I): PARTIAL
Availability (A): NONE
Additional information:

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