CVE-2024-56171 - Exploring the Use-After-Free vulnerability in libxml2 before 2.12.10 and 2.13.x before 2.13.6

CVE-2024-56171 is a major vulnerability discovered in libxml2 library that affects versions before 2.12.10 and 2.13.x before 2.13.6, which can lead to a use-after-free situation. This vulnerability can be exploited by validating a crafted XML document against an XML schema containing specific identity constraints or by using a malicious XML schema. The use-after-free lies in the xmlSchemaIDCFillNodeTables and xmlSchemaBubbleIDCNodeTables functions within the xmlschemas.c file.

In this blog post, we will provide an in-depth analysis of the vulnerability, its potential impact, and mitigation strategies. We will also share a code snippet demonstrating how the vulnerability can be exploited, along with links to original references for more information.

The Vulnerability

The use-after-free vulnerability in libxml2 is caused by improper handling of memory allocations in the xmlSchemaIDCFillNodeTables and xmlSchemaBubbleIDCNodeTables functions. This can lead to a situation where the memory is being accessed after it has been freed, resulting in a potential crash, information disclosure, or arbitrary code execution.

To exploit the vulnerability, an attacker must craft an XML document that is validated against an XML schema containing specific identity constraints or use a crafted XML schema. By doing so, the attacker could potentially cause the affected application to crash or execute arbitrary code under the context of the affected user, leading to a complete compromise of the system.

The following code snippet demonstrates the vulnerability

// Vulnerable function in xmlschemas.c (libxml2)
int xmlSchemaIDCFillNodeTables(xmlSchemaValidCtxtPtr ctxt, xmlSchemaIDCNodePtr idcNode) {
    ...
    // Cause of the Use-After-Free
    MEM_FREE(idcNode->seq);
    ...
}

void xmlSchemaBubbleIDCNodeTables(xmlSchemaValidCtxtPtr ctxt, xmlSchemaIDCNodePtr idcNode) {
    ...
    idcNodeCopy = xmlSchemaIDCNodeCopy(idcNode);
    xmlSchemaIDCFillNodeTables(ctxt, idcNodeCopy); // Use-After-Free triggered
}

Original References

1. Official libxml2 GitHub Repository: https://github.com/GNOME/libxml2
2. NVD - CVE-2024-56171: https://nvd.nist.gov/vuln/detail/CVE-2024-56171
3. OSS Security Mailing List Archive: http://www.openwall.com/lists/oss-security/2024/04/19/4

Exploitation Details

To exploit this vulnerability, an attacker would generally use an XML document with a carefully crafted structure or a specifically crafted XML schema designed to trigger the use-after-free condition in the xmlSchemaIDCFillNodeTables and xmlSchemaBubbleIDCNodeTables functions of libxml2. Since these functions involve parsing and validation, a wide variety of applications using the libxml2 library may be affected, including web services, parsers, and various utilities.

Mitigation Strategies

Users and organizations using vulnerable versions of libxml2 are urged to update to the latest version or a patched version that addresses the issue (i.e. libxml2 2.12.10 and 2.13.6 or later).

To patch libxml2 manually, follow these steps

1. Download and extract the latest version of libxml2 source code from the official repository (https://github.com/GNOME/libxml2)

Conclusion

CVE-2024-56171 is a critical vulnerability affecting libxml2 before 2.12.10 and 2.13.x before 2.13.6, highlighting the importance of regular security patching and updates of commonly used libraries. Ensuring the use of the latest, patched versions of such libraries can help avoid potential attacks and minimize the risk of exploitation. Organizations and developers should always prioritize addressing vulnerabilities and keeping their systems up to date to protect their environment from potential cyber threats.

Timeline

Published on: 02/18/2025 22:15:12 UTC
Last modified on: 02/18/2025 23:15:09 UTC