The Common Vulnerabilities and Exposures (CVE) system provides a reliable way of identifying and tracking vulnerabilities in software systems. This blog post details a vulnerability classified as CVE-2023-45918. This vulnerability is related to the ncurses library, specifically version 6.4-20230610, and it pertains to a NULL pointer dereference in the tgetstr function in the tinfo/lib_termcap.c file.

Background

The ncurses library is a widely-used library for writing text-based interfaces in terminal-based programs. It provides a robust API for developers to create rich, responsive text interfaces that are compatible with a wide range of terminal emulators and hardware. The tgetstr function is part of the termcap compatibility API of the ncurses library, which provides a means to interact with terminal capabilities in a standardized way.

Overview of the Vulnerability

A NULL pointer dereference vulnerability has been discovered in the tgetstr function, located in the tinfo/lib_termcap.c file. NULL pointer dereference vulnerabilities occur when a program attempts to access memory locations referenced by a NULL pointer, leading to undefined behavior, crashes, and potential security issues.

The vulnerability was introduced in version 6.4-20230610 of the ncurses library. The specific issue lies in the improper handling of certain inputs passed to the tgetstr function, which can cause a NULL pointer dereference. An attacker can potentially exploit this vulnerability to execute arbitrary code or cause a denial of service by crashing the affected software.

Code Snippet Demonstrating the Issue

Here's a code snippet that shows where the NULL pointer dereference occurs in the tgetstr function, found in the tinfo/lib_termcap.c file:

char *
tgetstr (char *name, char **buf)
{
    int i;
    TERMTYPE *tp;
    TPENTRY tpent;
    char *p;
    int code;

    // ... initialization code ...

    // Vulnerable section
    p = _nc_find_entry(_nc_fix_entry(NULL, name, &tpent), tp->StrTable);
    p = tp->StrTable[tp->extIndices[code = (p - tp->StrTable)]];
    
    // ... rest of the function ...
}

In the vulnerable section above, if _nc_find_entry returns NULL and name is not present in the StrTable, the assignment of p to tp->StrTable[tp->extIndices[code = (p - tp->StrTable)]] results in a NULL pointer dereference.

This vulnerability has been documented in the following online resources

1. The CVE entry for this vulnerability can be found at the CVE List maintained by the MITRE Corporation.
2. Further technical details and a report of the issue can be found in the ncurses mailing list at the following link.

To mitigate the potential impact of this vulnerability, follow these guidelines

1. Update the ncurses library to the latest available version that contains a fix for this vulnerability. Monitor the ncurses mailing list or updates from the developers.
2. Carefully validate and sanitize any inputs passed to the affected function(s), ensuring that only valid and trusted data is allowed to reach the vulnerable code.
3. Analyze and review the software design and implementation to find other potential vulnerabilities that may exist in the codebase.

Conclusion

As we have briefly discussed in this blog post, CVE-2023-45918 is a NULL pointer dereference vulnerability found in version 6.4-20230610 of the ncurses library. It specifically affects the tgetstr function in the tinfo/lib_termcap.c file. By staying vigilant and applying best practices to software design and development, we can ensure greater safety and security in the face of such vulnerabilities.

Timeline

Published on: 02/16/2024 22:15:07 UTC
Last modified on: 03/15/2024 11:15:08 UTC