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TI-2026-26987 Aliases CVE-2026-34743

XZ Utils: Buffer overflow in lzma_index_append()

Priority LOW 16CWE-122Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
—
Confidentiality · integrity · availability
None · None · Low
Fix status
Partial Red Hat: 7 fixed, 5 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00534 45th percentileScored 2026-11-07
Fix Partial xz (tukaani-project): 5.8.3Red Hat: 5 advisoriesRed Hat: 7 fixed, 5 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
tukaani-projectxzbefore 5.8.35.8.3Patch availableCNA
  • xz Vendortukaani-project Affected before 5.8.3 Fixed in 5.8.3 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:tukaani:xz:*:*:*:*:*:*:*:*before 5.8.3VulnerableTukaani
  • cpe:2.3:a:tukaani:xz:*:*:*:*:*:*:*:* Versions before 5.8.3 Vulnerable ·Tukaani

Remediation

  • Fix · CNA xz (tukaani-project) Fixed in 5.8.3

Red Hat 5 advisories

  • RHSA-2026:94802 Released 2026-11-04 · Red Hat rating Critical
    A Subscription Management tool for finding and reporting Red Hat product usage
    • Red Hat Discovery 2 registry.redhat.io/discovery/discovery-server-rhel9, registry.redhat.io/discovery/discovery-ui-rhel9
  • RHSA-2026:89749 Released 2026-10-26 · Red Hat rating Moderate
    xz security update
    • Red Hat Enterprise Linux AppStream (v. 9) xz-devel-5.2.5-8.el9_8.1, xz-lzma-compat-5.2.5-8.el9_8.1
    • Red Hat Enterprise Linux BaseOS (v. 9) xz-5.2.5-8.el9_8.1, xz-libs-5.2.5-8.el9_8.1
  • RHSA-2026:79357 Released 2026-10-08 · Red Hat rating Important
    Red Hat Cost Management On-Premise container image update
    • Red Hat Cost Management On-Premise 1 registry.redhat.io/costmanagement/costmanagement-ui-rhel10
Show 2 more Red Hat advisories
  • RHSA-2026:64787 Released 2026-09-08 · Red Hat rating Moderate
    xz security update
    • Red Hat Enterprise Linux AppStream (v. 10) xz-devel-1:5.6.2-4.el10_2.1, xz-lzma-compat-1:5.6.2-4.el10_2.1
    • Red Hat Enterprise Linux BaseOS (v. 10) xz-1:5.6.2-4.el10_2.1, xz-libs-1:5.6.2-4.el10_2.1
  • RHSA-2026:7647 Released 2026-04-11 · Red Hat rating Moderate
    Red Hat Hardened Images RPMs bug fix and enhancement update
    • Red Hat Hardened Images xz-5.8.3-1.1.hum1@aarch64, xz-5.8.3-1.1.hum1@src, xz-5.8.3-1.1.hum1@x86_64 +8

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Enterprise Linux 6AffectedNo fix planned: Out of support scope
Red Hat Enterprise Linux 7AffectedNo fix yet: Fix deferred
Red Hat Enterprise Linux 8AffectedNo fix yet: Fix deferred
Red Hat OpenShift AI (RHOAI)Affected—
Red Hat OpenShift Container Platform 4AffectedNo fix yet: Fix deferred
Red Hat Cost Management On-Premise 1Fixed RHSA-2026:79357
Red Hat Discovery 2Fixed RHSA-2026:94802
Red Hat Enterprise Linux AppStream (v. 10)Fixed RHSA-2026:64787
Red Hat Enterprise Linux AppStream (v. 9)Fixed RHSA-2026:89749
Red Hat Enterprise Linux BaseOS (v. 10)Fixed RHSA-2026:64787
Red Hat Enterprise Linux BaseOS (v. 9)Fixed RHSA-2026:89749
Red Hat Hardened ImagesFixed RHSA-2026:7647
Not affected: 1 product
  • Red Hat OpenShift AI (RHOAI)

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-34743
  2. 2026-10-09 Fix available: RHSA-2026:79357 · Red Hat
  3. 2026-10-09 Fix available: Red Hat Cost Management On-Premise 1 · Red Hat
  4. 2026-10-26 Fix available: RHSA-2026:89749 · Red Hat
  5. 2026-10-26 Fix available: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux BaseOS (v. 9) · Red Hat
  6. 2026-11-04 Fix available: RHSA-2026:94802 · Red Hat
  7. 2026-11-04 Fix available: Red Hat Discovery 2 · Red Hat
  8. 2026-11-06 Affected versions changed · Red Hat

References

Patch 2

Advisory 1

Other 1

  • TI-2025-22376 XZ has a heap-use-after-free bug in threaded .xz decoder CVSS 4.0HIGH 8.7
  • TI-2024-31891 XZ Utils on Microsoft Windows platform are vulnerable to argument injection CVSS 4.0MEDIUM 6.3

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences