CVE-2019-20202

Step 1: Malformed XML Input: The attacker crafts a malicious XML document designed to trigger the vulnerability. This document likely contains specific XML structures or content that, when parsed by ezXML, leads to the problematic memory operation in ezxml_char_content().

Step 2: Parsing Trigger: The vulnerable application, using ezXML, attempts to parse the malicious XML document.

Step 3: Function Invocation: The ezxml_char_content() function is called during the parsing process, processing the crafted XML content.

Step 4: Invalid Reallocation: Inside ezxml_char_content(), the code attempts to realloc a memory block that has not been correctly allocated or initialized.

Step 5: Segmentation Fault: The realloc operation, or subsequent memory access, triggers a segmentation fault due to the invalid memory access.

Step 6: Application Crash: The segmentation fault causes the application using ezXML to crash, resulting in a denial-of-service condition.

The vulnerability lies within the ezxml_char_content() function in ezXML versions 0.8.3 through 0.8.6. The function attempts to use realloc on a memory block that has not been properly allocated or initialized. This leads to undefined behavior, ultimately resulting in an invalid free operation. The root cause is a flaw in the memory management logic within the XML parsing process. The function incorrectly assumes the memory block is valid for reallocation, leading to a segmentation fault when the program attempts to access or modify the invalid memory region. This is not a buffer overflow or a remote code execution (RCE) vulnerability, but rather a denial-of-service (DoS) condition.