Researchers have discovered a use-after-free vulnerability in the ProcRenderAddGlyphs() function of Xorg servers (CVE-2024-31083). This flaw potentially allows an authenticated attacker to execute arbitrary code on the affected system. This post will provide an in-depth analysis of this vulnerability, including code snippets, references to the original sources, and details on potential exploits.

Vulnerability Details

The use-after-free issue occurs when AllocateGlyph() is called in the ProcRenderAddGlyphs() function of Xorg servers to store new glyphs sent by clients to the X server. This can result in multiple entries pointing to the same non-refcounted glyphs. Consequently, when ProcRenderAddGlyphs() frees a glyph, a use-after-free scenario may be triggered when the same glyph pointer is accessed later.

Here's a simplified code snippet illustrating the vulnerability

int ProcRenderAddGlyphs(RENDER_REQUEST *request) {
    GlyphPtr glyph;
    // [...]

    glyph = AllocateGlyph(request);

    // [...]

    if (glyph) {
        // [...]

        FreeGlyph(glyph);
        // Use-after-free vulnerability may occur here
    }
}

Exploit Details

An authenticated attacker could potentially exploit this vulnerability by sending a specially crafted request to the X server, leading to the execution of arbitrary code on the system. The following steps outline the attacker's approach:

The attacker's request contains overlapping entries pointing to the same glyph.

3. The ProcRenderAddGlyphs() function processes the request and might call the FreeGlyph() function on the same glyph more than once.
4. The attacker's request triggers a use-after-free scenario and leads to potential arbitrary code execution.

Original References

The vulnerability was initially reported by [Researcher's Name] from [Institution/Organization] and has been assigned the CVE ID CVE-2024-31083. Relevant links are provided below:

- CVE: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-31083

- X.Org Foundation: https://www.x.org/

Mitigations

Users are strongly advised to apply the latest patches and updates provided by the X.Org Foundation to mitigate this vulnerability. Additionally, system administrators should limit the number of authenticated users who have access to X server and monitor the system for any suspicious activities.

Conclusion

The CVE-2024-31083 use-after-free vulnerability discovered in the ProcRenderAddGlyphs() function of Xorg servers poses a serious risk, as it could enable an authenticated attacker to execute arbitrary code on the affected system. Users are urged to apply the latest patches and updates to their systems in order to protect their environment from potential exploitation of this vulnerability.

Timeline

Published on: 04/05/2024 12:15:37 UTC
Last modified on: 04/25/2024 18:15:08 UTC