CVE-2025-32414 - Out-of-bounds Memory Access in libxml2 Python API due to Incorrect Return Value

A critical vulnerability (CVE-2025-32414) has been identified in libxml2, a widely-used library for parsing XML files. The vulnerability affects versions of libxml2 before 2.13.8 and 2.14.x before 2.14.2, where out-of-bounds memory access can occur in the Python API (Python bindings) due to an incorrect return value. This can lead to various issues, including potential denial of service, information disclosure, or even arbitrary code execution.

This blog post will explain the workings of this vulnerability, provide an example code snippet, discuss proof-of-concept (PoC) exploits, and overview possible mitigations.

Vulnerability Details

The root cause of the vulnerability lies in the two functions, xmlPythonFileRead and xmlPythonFileReadRaw, within the Python bindings for libxml2. The problem is the difference between bytes and characters, leading to an incorrect return value, resulting in out-of-bounds memory access.

The issue can be observed in the following code snippet

static int
xmlPythonFileRead(PyObject *self, char *buffer, int len) {
    PyObject *args, *result;
    Py_ssize_t res;

    if (xmlPythonFileReadBuffer == NULL)
        return ();
    args = Py_BuildValue((char *) "(O,i)", self, len);
    result = PyEval_CallObject(xmlPythonFileReadBuffer, args);
    if (result == NULL)
        return (-1);
    res=;
    if (Py_SIZE(result) == len+1) {
        if (strncmp(buffer, PyBytes_AS_STRING(result), len+1) == )
	    res = Py_SIZE(result);
        else
	    res = -1;
    } else {
        res = -1;
    }
    Py_DECREF(args);
    Py_DECREF(result);
    return (res)
}

In this function, the return value for the read operation should be the number of bytes read. However, due to the difference between bytes and characters, the return value may sometimes be incorrect, leading to out-of-bounds memory access.

As a result, one can craft an example XML file to exploit this vulnerability, as demonstrated by the following PoC:

import libxml2

# the crafted XML file filename
file_path = "craft_xml_file.xml"

xml_doc = libxml2.parseFile(file_path)

# any arbitrary operation with xml_doc

In the example above, one can create a crafted XML file that triggers the vulnerability. As a result, there could be an out-of-bounds memory access when using the libxml2 Python API.

Mitigation

The best way to prevent this vulnerability is to update the libxml2 library to one of the fixed versions (either 2.13.8 or 2.14.2). Users should update their software or servers as necessary with these versions, to eliminate the possibility of exploitation.

Original References

1. CVE Details
2. libxml2 GitHub Repository
3. Patch: 2.13.8 Release
4. Patch: 2.14.2 Release

Conclusion

The CVE-2025-32414 vulnerability in the libxml2 Python API highlights the importance of keeping libraries and applications up-to-date. Users should ensure they are using the patched versions of libxml2 to eliminate the risk of out-of-bounds memory access and prevent potential security issues.

Timeline

Published on: 04/08/2025 03:15:15 UTC
Last modified on: 04/23/2025 19:09:35 UTC