Buffer overflow in Tukaani Xz
CVE-2026-34743
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.005 (42.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 42.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.001
Affected products
- Tukaani Xz
- Tukaani-Project Xz — versions < 5.8.3
Weakness classification (CWE)
References
- github.com/tukaani-project/xz/security/advisories/GHSA-x872-m794-cxhv (Vendor Advisory)
- github.com/tukaani-project/xz/commit/c8c22869e780ff57c96b46939c3d79ff99395f87 (Patch)
- github.com/tukaani-project/xz/releases/tag/v5.8.3 (Product, Release Notes)
- af854a3a-2127-422b-91ae-364da2661108 (Mailing List, Patch, Third Party Advisory)
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2026-34743?
- CVE-2026-34743 is a medium-severity vulnerability in Tukaani Xz, classified under Heap-based Buffer Overflow. CVSS score: 5.3/10. Published 2026-04-02.
- How severe is CVE-2026-34743?
- Medium severity. CVSS v3 base score is 5.3 out of 10.