CVE-2021-43784 vulnerability in Linux Foundation and Other Products
Published on December 6, 2021

Overflow in netlink bytemsg length field allows attacker to override netlink-based container configuration

runc is a CLI tool for spawning and running containers on Linux according to the OCI specification. In runc, netlink is used internally as a serialization system for specifying the relevant container configuration to the `C` portion of the code (responsible for the based namespace setup of containers). In all versions of runc prior to 1.0.3, the encoder did not handle the possibility of an integer overflow in the 16-bit length field for the byte array attribute type, meaning that a large enough malicious byte array attribute could result in the length overflowing and the attribute contents being parsed as netlink messages for container configuration. This vulnerability requires the attacker to have some control over the configuration of the container and would allow the attacker to bypass the namespace restrictions of the container by simply adding their own netlink payload which disables all namespaces. The main users impacted are those who allow untrusted images with untrusted configurations to run on their machines (such as with shared cloud infrastructure). runc version 1.0.3 contains a fix for this bug. As a workaround, one may try disallowing untrusted namespace paths from your container. It should be noted that untrusted namespace paths would allow the attacker to disable namespace protections entirely even in the absence of this bug.

Github Repository NVD

Vulnerability Analysis

CVE-2021-43784 is exploitable with network access, and requires small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be low. considered to have a small impact on confidentiality and integrity and availability.

Attack Vector:

NETWORK

Attack Complexity:

HIGH

Privileges Required:

LOW

User Interaction:

NONE

Scope:

CHANGED

Confidentiality Impact:

LOW

Integrity Impact:

LOW

Availability Impact:

LOW

Weakness Type

Integer Overflow or Wraparound

The software performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control. An integer overflow or wraparound occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may wrap to become a very small or negative number. While this may be intended behavior in circumstances that rely on wrapping, it can have security consequences if the wrap is unexpected. This is especially the case if the integer overflow can be triggered using user-supplied inputs. This becomes security-critical when the result is used to control looping, make a security decision, or determine the offset or size in behaviors such as memory allocation, copying, concatenation, etc.

Products Associated with CVE-2021-43784

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Linux Foundation Runc

Debian Linux

Canonical Ubuntu Linux

Affected Versions

opencontainers runc Version < 1.0.3 is affected by CVE-2021-43784

Exploit Probability

EPSS

0.12%

Percentile

30.07%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.