CVE-2019-20200

Step 1: Payload Delivery: The attacker crafts a malicious XML file containing a specific pattern of line endings designed to trigger the vulnerability. Step 2: File Ingestion: The vulnerable application, using the ezXML library, attempts to parse the malicious XML file. Step 3: Vulnerability Trigger: The ezxml_decode function, while normalizing line endings, encounters the crafted pattern. Step 4: Buffer Over-read: Due to incorrect memory handling, the function attempts to read beyond the allocated buffer on the heap. Step 5: Information Disclosure/DoS: The over-read either leaks sensitive information from memory or causes the application to crash, resulting in a denial-of-service.

The vulnerability lies within the ezxml_decode function of the ezXML library, specifically in the "normalize line endings" feature. The flaw stems from incorrect memory management when handling line endings within a crafted XML file. The library attempts to read beyond the allocated buffer, leading to a heap-based buffer over-read. This can expose sensitive data residing in memory, such as credentials, or potentially lead to a crash, resulting in a denial-of-service (DoS). The vulnerability is triggered when the library attempts to process a specially crafted XML file containing a specific pattern of line endings, causing the read operation to exceed the bounds of the allocated memory. The root cause is a lack of proper bounds checking during the line ending normalization process, allowing for an out-of-bounds read.