CVE-2021-29991

Ubuntu Security Notice USN-5248-1

Severity Score

8.1

*CVSS v3.1

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

*Multiple Sources

Exploited in Wild

*KEV

Decision

*SSVC

Descriptions

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.

Firefox aceptaba incorrectamente una nueva línea en un encabezado HTTP/3, interpretándola como dos encabezados separados. Esto permitía un ataque de división de encabezados contra servidores que usaban HTTP/3. Esta vulnerabilidad afecta a Firefox versiones anteriores a 91.0.1 y Thunderbird versiones anteriores a 91.0.1

Multiple security issues were discovered in Thunderbird. If a user were tricked into opening a specially crafted website in a browsing context, an attacker could potentially exploit these to cause a denial of service, obtain sensitive information, trick a user into accepting unwanted permissions, conduct header splitting attacks, conduct spoofing attacks, bypass security restrictions, confuse the user, or execute arbitrary code.

*Credits: N/A

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Attack Vector

Network

Attack Complexity

Medium

Authentication

None

Confidentiality

Partial

Integrity

Partial

Availability

None

* Common Vulnerability Scoring System

SSVC

Decision:-

Exploitation

Automatable

Tech. Impact

* Organization's Worst-case Scenario

Timeline

2021-04-01 CVE Reserved
2021-11-03 CVE Published
2024-08-03 CVE Updated
2025-04-12 EPSS Updated
---------- Exploited in Wild
---------- KEV Due Date
---------- First Exploit

CWE

CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

CAPEC

References (1)

URL	Tag	Source

URL	Date	SRC

URL	Date	SRC

URL	Date	SRC
https://www.mozilla.org/security/advisories/mfsa2021-37	2021-11-04

Affected Vendors, Products, and Versions

Vendor		Product				Version		Other		Status
Vendor	Product	Version	Other	Status	<-- -->	Vendor	Product	Version	Other	Status
Mozilla Search vendor "Mozilla"		Firefox Search vendor "Mozilla" for product "Firefox"				< 91.0.1 Search vendor "Mozilla" for product "Firefox" and version " < 91.0.1"		-		Affected
Mozilla Search vendor "Mozilla"		Thunderbird Search vendor "Mozilla" for product "Thunderbird"				< 91.0.1 Search vendor "Mozilla" for product "Thunderbird" and version " < 91.0.1"		-		Affected