CVE-2021-26221: 
Linux Debian vulnerability analysis and mitigation

The ezxml_new function in ezXML 0.8.6 and earlier contains a vulnerability related to out-of-bounds (OOB) write when opening XML files after exhausting the memory pool. This vulnerability was disclosed on February 8, 2021, and affects all versions of ezXML up to and including version 0.8.6 (NVD, CVE).

The vulnerability exists in the ezxml_new function implementation where there is incorrect handling of the value returned by calloc. The issue occurs at line 838 in ezxml.c, where a memset operation is performed on memory allocated by malloc without proper error checking. This vulnerability has been assigned a CVSS v3.1 Base Score of 8.1 (HIGH) and a CVSS v2.0 Base Score of 5.8 (MEDIUM). The weakness has been classified as CWE-787 (Out-of-bounds Write) (NVD).

The vulnerability can lead to out-of-bounds write attempts resulting in segmentation faults in cases of restrictive memory protection, or near NULL pointer overwrites in environments with limited memory restrictions, such as embedded systems. In embedded environments where near-zero memory areas are used to store device configuration, this vulnerability could potentially allow configuration data to be overwritten (SourceForge Bug).

The vulnerability can be triggered both locally and remotely, depending on how XML files are obtained and processed. Memory allocations are triggered during XML file opening, making the allocation error exploitable through crafted XML files. The vulnerability has been confirmed as exploitable and can be reproduced using ErrorSanitizer (SourceForge Bug).

The issue can be mitigated by implementing proper error handling for memory allocation failures. The recommended approach follows the SEI CERT C Coding Standard guideline ERR33-C, which suggests detecting and handling standard library errors appropriately. A patch has been proposed to address this specific instance, though it's noted that similar issues may exist in other parts of the codebase (SourceForge Bug).