CVE-2026-34743

XZ Utils: Buffer overflow in lzma_index_append()

MEDIUM
5.3
CVSS Score
Published: April 2, 2026 at 06:36 PM UTC
Updated: July 24, 2026 at 09:10 PM UTC
1 product affected across 1 vendorXz

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Severity
MEDIUM5.3
Exploit prediction
EPSS 0.5%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 5.8.3
Affected range stops below 5.8.3, so it looks safe — our inference, not a vendor statement

References (5)

x_refsource_MISCProductRelease Notes
Source: cverecord
https://github.com/tukaani-project/xz/releases/tag/v5.8.3
Mailing ListPatchThird Party Advisory
Source: af854a3a-2127-422b-91ae-364da2661108
http://www.openwall.com/lists/oss-security/2026/03/31/13
Source: af854a3a-2127-422b-91ae-364da2661108
https://lists.debian.org/debian-lts-announce/2026/07/msg00034.html

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
LOW
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-122

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