CVE-2022-24130 - XTerm Buffer Overflow Vulnerability with Sixel Support

A new vulnerability has been discovered in xterm, a widely used terminal emulator, which affects versions up to and including Patch 370. Identified as CVE-2022-24130, this vulnerability is a buffer overflow that can be exploited when Sixel support is enabled in xterm. This blog post aims to provide an in-depth analysis of the vulnerability, its implications, and exploit details. We will also provide code snippets and links to original references for a deeper understanding of the issue.

Background

XTerm is a terminal emulator for the X Window System, a popular graphical user interface framework for Unix and Unix-like systems. One of xterm's features is support for Sixel graphics, a pixel format that allows terminals to display bitmap graphics sent as text input. Although Sixel support is not enabled by default, it is frequently used by developers and system administrators who need to render images within their terminal environments.

Vulnerability Details

CVE-2022-24130 is a buffer overflow vulnerability related to the handling of Sixel graphics data in xterm. The vulnerability occurs in the set_sixel function in graphics_sixel.c. When xterm processes a specially crafted text input containing malformed Sixel data, the function miscalculates the allocation of required memory. Consequently, subsequent writes exceed the allocated memory boundary, leading to a buffer overflow.

The following code snippet from graphics_sixel.c demonstrates the vulnerable buffer allocation calculation (comments added for clarity):

void
set_sixel(unsigned expect, unsigned actual)
{
    if (expect >  && actual > ) {
        /* Calculate total size needed for allocation */
        size_t total = ((CellClip) expect)*((size_t) actual);
        if (total > text_size) {
            /* Allocate memory with total size */
            sixel_map = TypeRealloc(CharData, total, sixel_map);
            if (sixel_map != ) {
                text_limit = total;
                text_size = total;
            }
        }
    }
}

If an attacker can provide crafted text input to trigger the affected function, the outcome can range from xterm crashes to arbitrary code execution with the privileges of the xterm process.

Proof of Concept

A proof of concept (PoC) of the vulnerability is not provided here to avoid malicious use. However, interested readers can find more information from the original references and learn how to reproduce the issue or test for the vulnerability in their environment. Please use this information responsibly and ethically.

Mitigation and Solution

The vulnerability has been addressed in xterm Patch 371. Users are advised to update their xterm installations to the latest version, ensuring that they are protected against this exploit. If upgrading xterm is not immediately possible, a temporary workaround is to disable Sixel support in xterm by disabling the --enable-sixel-graphics compile-time option or launching xterm with the -ti vt340 command-line option.

Original References

1. CVE-2022-24130 Entry on NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-24130
2. XTerm Patch 371 Changelog: https://invisible-mirror.net/archives/xterm/xterm.log.html#xterm_371

Conclusion

CVE-2022-24130 is a critical vulnerability affecting xterm when Sixel support is enabled. Patch 371 addresses the issue, and users should ensure they are running the latest version of xterm. Understanding and mitigation of such vulnerabilities helps us keep our systems secure and robust against potential attacks.

If you have any questions about this vulnerability, its impact, or potential mitigation strategies, please do not hesitate to reach out to the community for assistance. Always ensure that your systems are up-to-date and patch regularly to protect against known vulnerabilities and improve overall system security.

Timeline

Published on: 01/31/2022 05:15:00 UTC
Last modified on: 08/19/2022 10:00:00 UTC