CVE-2024-31081: Heap-based Buffer Over-read Vulnerability in the X.org Server's ProcXIPassiveGrabDevice() Function

A heap-based buffer over-read vulnerability was recently discovered in the X.Org server's ProcXIPassiveGrabDevice() function. This issue emerges when byte-swapped length values are utilized in replies, potentially leading to memory leakage and segmentation faults, particularly when triggered by a client with a different endianness. The vulnerability could be exploited by an attacker, causing the X server to read heap memory values and transmitting them back to the client until an unmapped page is encountered, resulting in a crash. Though the attacker cannot control the specific memory copied into the replies, the small length values typically stored in a 32-bit integer can result in significant attempted out-of-bounds reads.

Code Snippet

The vulnerability is found in the following code from dix/devices.c in ProcXIPassiveGrabDevice() function:

/* If event and reply swap, adjust reply here */
if (client->swapped) {
    memcpy(tmpbuf, &reply.length, 4);
    swapl(&reply.length, n);
    WriteSwappedDataToClient(client, 32, &reply);
} else {
    WriteToClient(client, sizeof(xXIPassiveGrabDeviceReply), &reply);
}

Original References/Resources

1. X.Org Server's source code for dix/devices.c (where the vulnerability exists): Link.
2. Official X.Org website - containing updates and announcements regarding the X.org server: Link.
3. MITRE's CVE entry for this issue (CVE-2024-31081): Link.

Exploit Details

The vulnerability allows an attacker to read heap memory values by exploiting the ProcXIPassiveGrabDevice() function. Though the attacker cannot control the specific memory copied into the replies, the small length values typically stored in a 32-bit integer can result in a significant attempted out-of-bounds read. The memory leakage and segmentation faults are triggered by a client with different endianness, causing the X server to read heap memory values and transmitting them back to the client until an unmapped page is encountered, leading to an application crash.

To exploit this vulnerability, an attacker requires access to an affected X.Org server. They will proceed to send crafted requests to the server, causing it to use byte-swapped length values in replies. This action will permit the attacker to read heap memory content from the target server. The exploit may result in the discovery of sensitive information or cause the X server to crash, generating a denial-of-service (DoS) attack. However, the attacker will not be able to execute arbitrary code or bypass access controls because the read operations are limited to 32-bit integers.

Recommendations

It is highly recommended to make sure that your system is updated with the latest security patches released by your respective Linux distribution. These patches are created by developers to address vulnerabilities and improve system security continually. Additionally, implement strong access controls and network firewalls to limit exposure to potential attackers. Regularly inspect the software being used on your server to identify and rectify any discrepancies, ensuring your system remains secure.

Timeline

Published on: 04/04/2024 14:15:10 UTC
Last modified on: 04/30/2024 20:15:08 UTC