CVE-2025-49796: libxml2 Memory Corruption DoS Vulnerability

CVE-2025-49796 Overview

A vulnerability was found in libxml2. Processing certain sch:name elements from the input XML file can trigger a memory corruption issue. This flaw allows an attacker to craft a malicious XML input file that can lead libxml2 to crash, resulting in a denial of service or other possible undefined behavior due to sensitive data being corrupted in memory.

Critical Impact

This vulnerability can lead to denial of service and potential data corruption.

Affected Products

• Not Available

Discovery Timeline

• 2025-06-16 - CVE CVE-2025-49796 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-49796

Vulnerability Analysis

The vulnerability arises from improper handling of specific XML schema elements. An attacker can manipulate these elements to cause a buffer overflow that might corrupt memory, resulting in application crashes or other unstable behaviors.

Root Cause

The root cause is an insufficient bounds check when parsing sch:name elements from XML inputs, leading to an out-of-bounds write.

Attack Vector

This vulnerability can be exploited remotely over a network by sending crafted XML files to a system that uses libxml2 for XML parsing.

// Example exploitation code (sanitized)
#include <libxml/parser.h>

void trigger_vulnerability(const char *filename) {
    xmlDocPtr doc = xmlReadFile(filename, NULL, 0);
    if (doc == NULL) {
        fprintf(stderr, "Failed to parse %s\n", filename);
    }
    // Further processing that triggers the overflow...
    xmlFreeDoc(doc);
}

Detection Methods for CVE-2025-49796

Indicators of Compromise

• Unusual crashes of applications that utilize libxml2
• Logs showing exceptions or faults in XML parsing components
• System instability or unexpected behavior when handling XML data

Detection Strategies

Utilize heuristic detection methods to monitor and alert on patterns of exploitation such as repeated attempts to parse large and malformed XML files.

Monitoring Recommendations

Establish logging and monitoring of XML parsing activities within applications. Consider implementing abnormal XML file size alerts and logging stack traces of failed XML parsing.

How to Mitigate CVE-2025-49796

Immediate Actions Required

• Review and implement available patches from vendors
• Restrict access to XML parsing endpoints
• Enable application-level input validation to filter malformed XML files

Patch Information

Refer to vendor-specific guidance and apply the patches described in the Red Hat Security Advisory.

Workarounds

If immediate patching is not possible, consider filtering XML inputs to remove or sanitize sch:name elements before processing.

# Configuration example
sed -i '/<sch:name>/d' input.xml