A critical buffer overflow flaw (CVE-2025-26597) has been identified in the X.Org and Xwayland software that could potentially allow attackers to execute arbitrary code within the vulnerable systems. This vulnerability is present in the XkbChangeTypesOfKey() function, which could lead to a buffer overflow issue if not appropriately addressed. In this post, we'll delve deep into the vulnerability, discuss its exploit details, provide code snippets, and link the original references to help the community understand and mitigate this potential security threat.

Exploit Details

The CVE-2025-26597 vulnerability exists in the X.Org and Xwayland software, which are responsible for providing an open-source implementation of the X Window System. The flaw revolves around the function XkbChangeTypesOfKey(), which is responsible for changing the types of keys in a keyboard.

The issue occurs when XkbChangeTypesOfKey() is called with a "groups" value, which results in resizing the key symbols table to but doesn't change the key actions. When the same function is invoked later with a non-zero "groups" value, this results in a buffer overflow. The buffer overflow happens as the key actions are of the wrong size, thus leading to unintended data being overwritten, potentially allowing an attacker to execute arbitrary code within the vulnerable system.

The following code snippet demonstrates the buffer overflow vulnerability

static Bool
#if NeedFunctionPrototypes
IllegalTypeForKey(KeyTypePtr type, XkbKeyTypePtr key_types, int num_types)
#else
IllegalTypeForKey(type, key_types, num_types)
    KeyTypePtr type;
    XkbKeyTypePtr key_types;
    int num_types;
#endif
{
    ...
}
Bool
#if NeedFunctionPrototypes
XkbChangeKeyType(XkbDescPtr xkb, KeyCode key, int nz_groups, int options)
#else
XkbChangeKeyType(xkb, key, nz_groups, options)
    XkbDescPtr xkb;
    KeyCode key;
    int nz_groups;
    int options;
#endif
{
    ...
}

Mitigation

The developers of X.Org and Xwayland have acknowledged this vulnerability and are working on a patch to address the issue. Administrators should apply the patch once it is available to prevent any possible exploitation by malicious actors.

Furthermore, it is strongly recommended to follow general security best practices like restricting access to critical systems and updating all software to the latest versions available.

Original References

1. X.Org website: https://www.x.org/wiki/
2. Xwayland repository: https://gitlab.freedesktop.org/xorg/xserver/-/tree/master/hw/xwayland
3. X.Org security advisory: https://lists.x.org/archives/xorg/2025-January/012499.html

Conclusion

The CVE-2025-26597 buffer overflow vulnerability in X.Org and Xwayland is a critical issue that can result in attackers executing arbitrary code in the affected systems. By understanding the exploit mechanism and staying updated with the patches released by the developers, administrators can better protect their systems and data from possible attacks. Remember to follow general security best practices and always stay vigilant to potential security concerns.

Timeline

Published on: 02/25/2025 16:15:38 UTC
Last modified on: 03/21/2025 17:50:53 UTC