CVE-2026-34743: tukaani-project xz Heap-based Buffer Overflow

Vulnerability summary

CVE-2026-34743 is a medium (CVSS 5.3) Heap-based Buffer Overflow vulnerability in tukaani-project xz. EPSS estimates a 0.51% chance of exploitation in the next 30 days, higher than 42.6% of scored vulnerabilities.

Timeline

1. 02-04-2026
   PublishedVulnerability first disclosed.
2. 21-07-2026
   Last modifiedVulnerability information updated.

Description

XZ Utils provide a general-purpose data-compression library plus command-line tools. Prior to version 5.8.3, if lzma_index_decoder() was used to decode an Index that contained no Records, the resulting lzma_index was left in a state where where a subsequent lzma_index_append() would allocate too little memory, and a buffer overflow would occur. This issue has been patched in version 5.8.3.

• CWE-122Heap-based Buffer OverflowA heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().