The Common Vulnerabilities and Exposures (CVE) database has recently reported a security vulnerability related to stack-based buffer overflows in cifs-utils, specifically version 6.14. This vulnerability, documented as CVE-2022-27239, could allow a local attacker to gain root privileges. In this long-read post, we provide a detailed explanation of the CVE-2022-27239 vulnerability, including code snippets, original references, and exploit details.

Vulnerability Details

cifs-utils is a collection of tools for managing and mounting Common Internet File System (CIFS) shares. It is widely used for providing access to shared file systems over the network. The vulnerability occurs in the handling of the mount.cifs ip= command-line argument.

The developers of cifs-utils missed a crucial check on the size of the provided IP address when parsing the "ip=" command-line argument, which allows an attacker to exploit this vulnerability by creating a specially crafted command featuring an overly long IP address when mounting a CIFS share.

(Code snippet)

...
#define SERVER_NAME_LENGTH 256
...

int parse_unc(...)
{
    ...
    strncpy(source, value, SERVER_NAME_LENGTH);
    ...
}

In the code snippet above, the length of the source variable is defined with a constant length (SERVER_NAME_LENGTH) of 256. However, the value is not properly checked against the constant length (SERVER_NAME_LENGTH) before it is copied into the source variable. This oversight leads to a stack-based buffer overflow if the value exceeds 256 characters.

Here are the basic steps required for a potential exploitation of the buffer overflow vulnerability

1. An attacker prepares an overly long IP address. The IP address size must be greater than (256+1) in order to trigger the buffer overflow.

2. The attacker crafts a specially designed command-line argument with the oversized IP address for the mount.cifs command.

3. When executing the command, the application attempts to copy the oversized IP address into the source variable, causing the stack-based buffer overflow and overwriting the return address on the stack.

4. The attacker can redirect the execution flow and potentially execute arbitrary code with root privileges.

Protective Measures

Patching your system is the easiest and most effective way to protect yourself from this vulnerability. Users must update to the most recent version of cifs-utils (version 6.15 or newer) to address this vulnerability. The patch release ensures that the IP address length is properly validated before copying it into the source buffer.

(Reference to the patch that addresses the CVE-2022-27239 vulnerability: cifs-utils 6.15 patch)

To prevent a similar vulnerability from occurring in the future, developers should always validate user inputs for length and ensure that memory buffers are properly sized.

Conclusion

The CVE-2022-27239 vulnerability demonstrates the importance of proper input validation and memory management in software development. For users of cifs-utils version 6.14, it is crucial to apply the security patch as soon as possible to mitigate the risk of a stack-based buffer overflow that could potentially lead to root privilege escalation. Developers should learn from the mistake that led to this vulnerability, and always ensure robust input checking and memory allocation in their applications.

Original References

1. CVE-2022-27239: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-27239
2. cifs-utils 6.15 patch: https://git.samba.org/cifs-utils.git/?p=cifs-utils.git;a=commit;h=2b765f2b7bce96c1a3d7eccb6ddb4eb61a0342db

Timeline

Published on: 04/27/2022 14:15:00 UTC
Last modified on: 06/03/2022 15:15:00 UTC