Source: cve@mitre.org
An issue was discovered in ezXML 0.8.3 through 0.8.6. The function ezxml_char_content() tries to use realloc on a block that was not allocated, leading to an invalid free and segmentation fault.
ezXML, a library for parsing XML, is vulnerable to a denial-of-service (DoS) condition due to a memory management flaw. Specifically, the ezxml_char_content() function attempts to realloc memory on an uninitialized block, leading to an invalid free and a segmentation fault, effectively crashing the application. This vulnerability can be triggered by processing specially crafted XML documents.
Step 1: Malformed XML Input: A specially crafted XML document is provided as input to an application that uses the ezXML library. This document is designed to trigger the vulnerable code path in ezxml_char_content().
Step 2: Parsing Trigger: The application, using the ezXML library, attempts to parse the malicious XML document.
Step 3: Vulnerable Function Call: The ezxml_char_content() function is called during the parsing process, processing the crafted XML content.
Step 4: Incorrect Memory Operation: Inside ezxml_char_content(), the realloc function is called on a memory block that is either uninitialized or has been corrupted.
Step 5: Invalid Free: The incorrect memory operation leads to a subsequent attempt to free an invalid memory location.
Step 6: Segmentation Fault: The invalid free operation triggers a segmentation fault, causing the application to crash and resulting in a denial-of-service condition.
The vulnerability lies within the ezxml_char_content() function of the ezXML library. This function is responsible for handling character content within XML elements. The root cause is an incorrect memory management operation. The function attempts to use realloc on a memory block that has not been properly allocated or initialized. This can happen when the XML parser encounters certain malformed or crafted XML structures. When realloc is called on an uninitialized block, it can lead to undefined behavior, including an invalid free operation. The subsequent attempt to free this invalid memory region results in a segmentation fault, causing the application using the ezXML library to crash. This is a classic example of a use-after-free vulnerability, although in this case, it's more accurately described as an attempt to realloc an uninitialized memory region, which then leads to an invalid free.
While no specific APT groups are known to be actively exploiting this vulnerability, the availability of a PoC and the ease of exploitation make it a potential target for various threat actors. The impact is primarily a denial-of-service, which can be disruptive. Not listed on CISA KEV.
Monitor application logs for segmentation faults or crashes, especially when parsing XML documents.
Implement intrusion detection system (IDS) rules to identify attempts to exploit the vulnerability. These rules can be based on the characteristics of the malformed XML input.
Analyze core dumps or crash reports to identify the ezxml_char_content() function as the source of the crash.
Network traffic analysis: Look for unusual XML document sizes or structures, especially those exceeding typical document size limits.
Monitor for repeated attempts to access XML parsing functionality, which could indicate an active exploitation attempt.
Upgrade to a patched version of ezXML (0.8.7 or later).
Implement input validation to sanitize and validate XML documents before parsing them. This can help prevent malicious XML documents from reaching the vulnerable code.
Use a different XML parsing library that is not vulnerable to this issue.
Apply memory safety checks and hardening techniques to the application to mitigate the impact of memory-related vulnerabilities.
Regularly update all dependencies, including XML parsing libraries, to the latest versions to address known vulnerabilities.