CVE-2024-31080: Heap-Based Buffer Over-Read Vulnerability Found in X.org Server's ProcXIGetSelectedEvents() Function

Heap-based buffer over-read vulnerabilities pose a serious threat to the security and stability of applications and systems. The X.org server is a popular open-source implementation of the X Window System, which provides the graphical capabilities necessary for desktop environments on Unix and Unix-like operating systems. In this post, we describe a heap-based buffer over-read vulnerability discovered in the X.org server's ProcXIGetSelectedEvents() function (CVE-2024-31080) and discuss the potential exploitation of this flaw.

Vulnerability Details

The vulnerability exists in the ProcXIGetSelectedEvents() function of the X.org server, which handles the reading of selected events in the system. The issue occurs when byte-swapped length values are used in replies, leading to memory leakage and segmentation faults. This flaw is particularly dangerous when triggered by a client with a different endianness, as it could result in significant attempted out-of-bounds reads, causing the X server to read heap memory values and transmit them back to the client until encountering an unmapped page. Ultimately, this can crash the server. It is important to note that while the attacker cannot control the specific memory copied into the replies, the small length values typically stored in a 32-bit integer can still cause significant risks.

The following code snippet demonstrates the heap-based buffer over-read vulnerability in action

void ProcXIGetSelectedEvents(ClientPtr client)
{
    // ...
    unsigned int length = bytes_to_int32(rep.length); // Byte-swapped length
    // ...

    if (client->swapped)
    {
        // ...
        swapl(&length);
        // ...
    }

    WriteToClient(client, sz_xGetXISelectedEventsReply + rep.length, (char *)&rep);

    // ...
}

As we can see, the code reads the byte-swapped length value (rep.length) from the client, which is then passed to the WriteToClient() function. If the client is of a different endianness, the length value is swapped again, causing the memory leakage and segmentation faults mentioned earlier.

Original References

The vulnerability has been assigned the CVE ID CVE-2024-31080. Further information about this vulnerability can be found in the official CVE advisory: CVE-2024-31080 Advisory

A detailed description of the vulnerability and its consequences is also available at the X.org security mailing list archive: X.org Security Mailing List

Mitigation

To mitigate this vulnerability, it is recommended to apply the patches provided by the X.org project, ensuring that the X server software is updated to the latest version. Additionally, system administrators should keep their operating systems and all software packages up to date to prevent potential exploitation. Monitoring system logs for signs of unauthorized access or suspicious activity is also crucial in detecting potential security breaches.

Conclusion

Heap-based buffer over-read vulnerabilities like the one found in the X.org server's ProcXIGetSelectedEvents() function are significant risks that can compromise system stability and security. By understanding the risks associated with CVE-2024-31080, applying patches and maintaining up-to-date software, administrators can help protect their systems from potential exploits.

Timeline

Published on: 04/04/2024 14:15:10 UTC
Last modified on: 04/29/2024 19:15:20 UTC