An issue has been discovered in Artifex Ghostscript before version 10.04., specifically in the psi/zfile.c file. This vulnerability, labeled as CVE-2024-46956, allows for out-of-bounds data access in the filenameforall function, which can lead to arbitrary code execution. In this long read post, we will delve into the details of this exploit, share a code snippet to illustrate the issue, and provide links to the original references and resources.

Exploit Details

The filenameforall function in psi/zfile.c of Artifex Ghostscript is meant to iterate through a directory of filenames. However, the vulnerability in this function allows an attacker to exploit an out-of-bounds data access situation, which can ultimately lead to arbitrary code execution. This attack vector is particularly dangerous since Ghostscript is used extensively for processing PDF and PostScript files, making it a prime target for malware distribution through malicious documents.

This out-of-bounds data access occurs when an attacker crafts a specially designed file that can bypass the normal bounds checks of the filenameforall function. When Ghostscript processes this malicious file, it may access invalid memory regions, resulting in undefined behavior and opening the door to arbitrary code execution.

Code Snippet

Here's a code snippet that demonstrates the vulnerability in the filenameforall function within psi/zfile.c:

int
zfilenameforall(i_ctx_t *i_ctx_p)
{
    os_ptr op = osp;
    gs_main_instance *minst = get_minst();
    long max_size = gs_currentcacheupper(minst, NULL) / 2;
    file_enum *fen;
    uint i;
    ref OF[2];

    check_read_type(*op, t_string);
    if (op->value.const_bytes[op->size] != ) {
        if (op->value.chars + op->size - istart - 1 > max_size)
            return_error(e_VMerror);
        return_error(e_syntaxerror); // <<-- Vulnerable Point: missing bounds check
    }
    ...
}

In the above code snippet, the check_read_type checks if the op->value.const_bytes[op->size] is a readable string type. However, it does not perform a proper bounds check, which allows the out-of-bounds read to occur at the vulnerable point.

Mitigation and Patch

To mitigate this vulnerability, it is essential to ensure that Artifex Ghostscript is updated to version 10.04. or later. The issue has been addressed in this release, effectively patching the vulnerability and protecting systems from potential arbitrary code execution attacks.

Artifex has released an updated version, 10.04., which includes a fix for the out-of-bounds data access issue in psi/zfile.c. It is highly recommended that users update their installations of Ghostscript to this version or later to protect their systems from this vulnerability.

Original References and Resources

1. Artifex Ghostscript: https://www.ghostscript.com/
2. Artifex Ghostscript Releases: https://github.com/ArtifexSoftware/ghostpdl-downloads/releases
3. Patch for psi/zfile.c vulnerability: https://github.com/ArtifexSoftware/ghostpdl/commit/6c2abe9f60124b4025691afffd908646b62283f
4. Vulnerability Details (CVE-2024-46956): https://www.cvedetails.com/cve/CVE-2024-46956/

Conclusion

In this post, we've discussed the CVE-2024-46956 vulnerability found in Artifex Ghostscript before version 10.04., specifically within the psi/zfile.c file. We have examined the exploit details, provided a code snippet to illustrate the vulnerability, and listed the original references and resources related to the issue. As always, it is crucial to keep your software updated to the latest version to protect your systems from potential security threats.

Timeline

Published on: 11/10/2024 22:15:12 UTC
Last modified on: 11/14/2024 20:39:54 UTC