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NVD / CVE Program· CNA GitHub_M

CVE-2026-34743: XZ Utils: Buffer overflow in lzma_index_append()

Noroxi assessment

Priority: Monitor (action score 6/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.53% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: tukaani-project xz 5.8.3; azl3 rust 1.75.0-27 on Azure Linux 3.0 1.75.0-28; azl3 rust 1.90.0-6 on Azure Linux 3.0 1.90.0-7.

Low priority for now. Upgrade to tukaani-project xz 5.8.3; azl3 rust 1.75.0-27 on Azure Linux 3.0 1.75.0-28; azl3 rust 1.90.0-6 on Azure Linux 3.0 1.90.0-7 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

LowCVSS 1.7 · v4.0—No exploit Fix available
Published
Apr 2, 2026
Updated
Jul 24, 2026
EPSS
0.5% · 45th percentile

Report tools

JSON

Action score

6

Monitor

Low priority for now.

CVSS
6 / 40 · 1.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.5%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
1.7
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-34743

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
tukaanixz

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • tukaani xzbefore 5.8.3

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • tukaani-project xz

    • < 5.8.3affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:10xzbefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
AlmaLinux:10xz-develbefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
AlmaLinux:10xz-libsbefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
AlmaLinux:10xz-lzma-compatbefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
AlmaLinux:9xzbefore 5.2.5-8.el9_8.15.2.5-8.el9_8.1
AlmaLinux:9xz-develbefore 5.2.5-8.el9_8.15.2.5-8.el9_8.1
AlmaLinux:9xz-libsbefore 5.2.5-8.el9_8.15.2.5-8.el9_8.1
AlmaLinux:9xz-lzma-compatbefore 5.2.5-8.el9_8.15.2.5-8.el9_8.1
Alpine:v3.20xzbefore 5.8.3-r05.8.3-r0
Debian:12xz-utilsbefore 5.4.1-1+deb12u15.4.1-1+deb12u1
Debian:13xz-utilsbefore 5.8.1-1+deb13u15.8.1-1+deb13u1
Debian:14xz-utilsbefore 5.8.3-15.8.3-1
openSUSE:Tumbleweedxzbefore 5.8.3-1.15.8.3-1.1
Red Hat:enterprise_linux:10.2xzbefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
Red Hat:enterprise_linux:10.2xz-debuginfobefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
Red Hat:enterprise_linux:10.2xz-debugsourcebefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
Red Hat:enterprise_linux:10.2xz-develbefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
Red Hat:enterprise_linux:10.2xz-libsbefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
Red Hat:enterprise_linux:10.2xz-libs-debuginfobefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
Red Hat:enterprise_linux:10.2xz-lzma-compatbefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
Red Hat:enterprise_linux:10.2xz-lzma-compat-debuginfobefore 1:5.6.2-4.el10_2.11:5.6.2-4.el10_2.1
Red Hat:hummingbird:1xzbefore 0:5.8.3-1.1.hum10:5.8.3-1.1.hum1
Red Hat:hummingbird:1xz-develbefore 0:5.8.3-1.1.hum10:5.8.3-1.1.hum1
Red Hat:hummingbird:1xz-libsbefore 0:5.8.3-1.1.hum10:5.8.3-1.1.hum1

+4

Same product

tukaani: all records

Other highest-scoring records for the same primary product.

  • CVE-2024-3094Xz: malicious code in distributed source
    67This week
  • CVE-2015-4035scripts/xzgrep.in in xzgrep 5.2.x before 5.2.0, before 5.0.0 does not properly process file names containing semicolons, which allows remote
    31Monitor
  • CVE-2020-22916An issue discovered in XZ 5.2.5 allows attackers to cause a denial of service via decompression of a crafted file.
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
tukaani-project xz5.8.3 · descriptionVendor (CNA)
azl3 rust 1.75.0-27 on Azure Linux 3.01.75.0-28 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 rust 1.90.0-6 on Azure Linux 3.01.90.0-7 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 xz 5.4.4-2 on Azure Linux 3.05.4.4-3 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 xz 5.4.4-3 on Azure Linux 3.05.4.4-3 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 cmake 3.21.4-23 on CBL-Mariner 2.0Release NotesMicrosoft (MSRC)
cbl2 rust 1.72.0-15 on CBL Mariner 2.01.72.0-16 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 rust 1.72.0-15 on CBL-Mariner 2.01.72.0-16 · Release NotesMicrosoft (MSRC)
cbl2 xz 5.2.5-1 on CBL Mariner 2.05.2.5-2 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 xz 5.2.5-1 on CBL-Mariner 2.05.2.5-2 · Release NotesMicrosoft (MSRC)
almalinux:xz1:5.6.2-4.el10_2.1 · AlmaLinux:10Package registry (OSV)
almalinux:xz-devel1:5.6.2-4.el10_2.1 · AlmaLinux:10Package registry (OSV)
almalinux:xz-libs1:5.6.2-4.el10_2.1 · AlmaLinux:10Package registry (OSV)
almalinux:xz-lzma-compat1:5.6.2-4.el10_2.1 · AlmaLinux:10Package registry (OSV)
alpine:xz5.8.3-r0 · Alpine:v3.20Package registry (OSV)
debian:xz-utils5.4.1-1+deb12u1 · Debian:12Package registry (OSV)
opensuse:xz5.8.3-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:xz1:5.6.2-4.el10_2.1 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:xz-debuginfo1:5.6.2-4.el10_2.1 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:xz-debugsource1:5.6.2-4.el10_2.1 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:xz-devel1:5.6.2-4.el10_2.1 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:xz-libs1:5.6.2-4.el10_2.1 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:xz-libs-debuginfo1:5.6.2-4.el10_2.1 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:xz-lzma-compat1:5.6.2-4.el10_2.1 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:xz-lzma-compat-debuginfo1:5.6.2-4.el10_2.1 · Red Hat:enterprise_linux:10.2Package registry (OSV)
red hat:xz-static0:5.8.3-1.1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
rocky linux:xz1:5.6.2-4.el10_2.1 · Rocky Linux:10Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-122 · Heap-based Buffer Overflow

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records