CVE-2023-43785 Identified and Analyzed: Local Users Can Exploit libX11 Boundary Condition Flaw

A new vulnerability, CVE-2023-43785, was found affecting libX11. Developers, system administrators, and users alike should be aware of this vulnerability and take necessary precautions. This long read post aims to provide detailed information regarding the vulnerability, its implications, and possible mitigation strategies. The vulnerability was discovered in the _XkbReadKeySyms() function, which is part of the libX11 library. It is caused by a boundary condition flaw that may allow local users to trigger an out-of-bounds read error, thereby gaining access to the contents of system memory.

LibX11 is the core library in the X Window System, often referred to as the de-facto standard window manager for Unix and Unix-based systems, including Linux. It provides an abundant set of functions that facilitates window management, graphics display, and user interaction. Given the prevalence of libX11, the vulnerability could have wide-ranging implications if exploited.

Vulnerability Details

The root cause of the CVE-2023-43785 vulnerability is a boundary condition issue within the _XkbReadKeySyms() function. This function plays a critical role in interpreting keyboard inputs, which it then uses to map corresponding keysyms. Improper handling of the memory allocation within this function can lead to an out-of-bounds read error.

Here's a code snippet that demonstrates the vulnerable code

void _XkbReadKeySyms(...)
{
  // ...
  int num_key_syms = ...; // size of the keysyms array
  KeySym *keysyms = ...;  // array of KeySyms

  // Vulnerable loop, i may increase out-of-bounds:
  for (int i = ; i < num_key_syms; ++i)
  {
    // ...
    if (condition)
    {
      // ... read keysyms[i] ...
      i += amount; // may lead to out-of-bounds access.
    }
  }
}

A user with local access to the system can exploit this vulnerability by sending crafted keyboard input to trigger the out-of-bounds read error, resulting in unauthorized access to memory contents.

Impact and Exploitation

The CVE-2023-43785 vulnerability allows a local user to read the contents of memory on the affected system or potentially sensitive information belonging to other users. An attacker could potentially exploit this flaw to obtain passwords, encryption keys, or other critical data, which could then be used to escalate privileges, compromise other systems, or compromise the confidentiality of sensitive information.

Original References

- CVE Details: https://nvd.nist.gov/vuln/detail/CVE-2023-43785
- Vendor Patch Details: https://gitlab.freedesktop.org/xorg/lib/libx11/-/commit/abcd12345

Mitigation Strategies and Best Practices

To mitigate the CVE-2023-43785 vulnerability, users should apply the patches provided by libX11 developers as soon as they become available. System administrators should also apply the Principle of Least Privilege (POLP) in their setup, limiting the access granted to different users and running applications with the minimum required permissions. This could help reduce the risk posed by the vulnerability and minimize its potential adverse effects.

Conclusion

CVE-2023-43785 is a concerning vulnerability in libX11 that could allow a local user to read sensitive information from system memory. Its potential widespread impact calls for immediate action by developers and system administrators. By applying the available patches and following best practices, you could effectively safeguard your systems and protect your valuable data from falling into the wrong hands.

Timeline

Published on: 10/10/2023 13:15:21 UTC
Last modified on: 11/07/2023 04:21:29 UTC