CVE Vulnerabilities

CVE-2021-29991

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

Published: Nov 03, 2021 | Modified: Nov 04, 2021
CVSS 3.x
8.1
HIGH
Source:
NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
CVSS 2.x
5.8 MEDIUM
AV:N/AC:M/Au:N/C:P/I:P/A:N
RedHat/V2
RedHat/V3
7.5 IMPORTANT
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Ubuntu
MEDIUM

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.

Weakness

The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.

Affected Software

Name Vendor Start Version End Version
Firefox Mozilla * 91.0.1 (excluding)
Thunderbird Mozilla * 91.0.1 (excluding)
Firefox Ubuntu bionic *
Firefox Ubuntu devel *
Firefox Ubuntu focal *
Firefox Ubuntu hirsute *
Firefox Ubuntu impish *
Firefox Ubuntu jammy *
Firefox Ubuntu kinetic *
Firefox Ubuntu lunar *
Firefox Ubuntu mantic *
Firefox Ubuntu noble *
Firefox Ubuntu trusty *
Firefox Ubuntu upstream *
Firefox Ubuntu xenial *
Mozjs38 Ubuntu bionic *
Mozjs38 Ubuntu esm-apps/bionic *
Mozjs38 Ubuntu upstream *
Mozjs52 Ubuntu bionic *
Mozjs52 Ubuntu esm-apps/focal *
Mozjs52 Ubuntu esm-infra/bionic *
Mozjs52 Ubuntu focal *
Mozjs52 Ubuntu upstream *
Mozjs68 Ubuntu focal *
Mozjs68 Ubuntu upstream *
Mozjs78 Ubuntu esm-apps/jammy *
Mozjs78 Ubuntu hirsute *
Mozjs78 Ubuntu impish *
Mozjs78 Ubuntu jammy *
Mozjs78 Ubuntu kinetic *
Mozjs78 Ubuntu lunar *
Mozjs78 Ubuntu upstream *
Thunderbird Ubuntu bionic *
Thunderbird Ubuntu focal *
Thunderbird Ubuntu hirsute *
Thunderbird Ubuntu trusty *
Thunderbird Ubuntu upstream *
Thunderbird Ubuntu xenial *

Extended Description

HTTP requests or responses (“messages”) can be malformed or unexpected in ways that cause web servers or clients to interpret the messages in different ways than intermediary HTTP agents such as load balancers, reverse proxies, web caching proxies, application firewalls, etc. For example, an adversary may be able to add duplicate or different header fields that a client or server might interpret as one set of messages, whereas the intermediary might interpret the same sequence of bytes as a different set of messages. For example, discrepancies can arise in how to handle duplicate headers like two Transfer-encoding (TE) or two Content-length (CL), or the malicious HTTP message will have different headers for TE and CL. The inconsistent parsing and interpretation of messages can allow the adversary to “smuggle” a message to the client/server without the intermediary being aware of it. This weakness is usually the result of the usage of outdated or incompatible HTTP protocol versions in the HTTP agents.

Potential Mitigations

References