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

unknownCVE-2026-34743

CSIRTS triage

vendor: XZ Utils product: XZ Utils Memory corruption

What: Buffer overflow in lzma_index_append() function.
Who is affected: All users of XZ Utils processing untrusted compressed data.
Urgency: Moderate; severity unknown but buffer overflows are typically serious and may enable code execution.
Action: Update to a patched version of XZ Utils when available.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: unknown
Published: 2026-08-06
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-34743

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-347430.45% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 37% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-34743	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

high[UPDATE] [high] xz: Vulnerability allows code executioncert-bund

Recent advisories for XZ Utils

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

criticalXZ Utils vulnerability impacting B&R Productscisa · 2026-06-30