Microsoft Windows libarchive: Heap-based buffer overflow enables code execution
Summary
A heap-based buffer overflow in the libarchive component of Windows allows an unauthorized attacker to execute code over a network. No authentication or user interaction is required according to the CVSS vector, and the CVSS base score is 9.8 (critical). Microsoft lists multiple Windows 10, Windows 11 and Windows Server versions as affected, but the network service that exposes libarchive is not documented in the sources reviewed.
Affected
- Windows 10 Version 1809 (10.0.17763.0 to below 10.0.17763.9376)
- Windows 10 Version 21H2 (10.0.19044.0 to below 10.0.19044.7807)
- Windows 10 Version 22H2 (10.0.19045.0 to below 10.0.19045.7807)
- Windows 11 Version 23H2 (10.0.22631.0 to below 10.0.22631.7652)
- Windows 11 Version 24H2 (10.0.26100.0 to below 10.0.26100.9711)
- Windows 11 Version 25H2 (10.0.26200.0 to below 10.0.26200.9711)
- Windows 11 Version 26H1 (10.0.28000.0 to below 10.0.28000.3231)
- Windows 11 Version 26H2 (10.0.26300.0 to below 10.0.26300.9711)
- Windows Server 2019 incl. Server Core (10.0.17763.0 to below 10.0.17763.9376)
- Windows Server 2022 (10.0.20348.0 to below 10.0.20348.5761)
- Windows Server 2025 incl. Server Core (10.0.26100.0 to below 10.0.26100.33650)
Fixed in
- Fixed in the October 2026 cumulative update (Patch Tuesday, October 13, 2026).
- Build numbers above are taken from the CNA record and third-party aggregators and must be verified against the MSRC affected products table before deployment.
- The exact KB number for Windows 10 1809 is unknown.
- Windows 10 22H2 build numbers differ between sources (19045.7807 vs. 19044.7807); verify before relying on them.
Workaround
Unknown. No workaround or mitigation is documented in the sources reviewed; patching is the documented remedy.
Exploitation
- No evidence of exploitation in the wild was found in the sources reviewed; check the CISA KEV catalogue directly.
- No public proof-of-concept code was found.
- CISA SSVC: Exploitation none, Automatable yes, Technical Impact total.
- EPSS 0.0079 (Vulners), a low probability of exploitation within 30 days.
Our recommendation
- Inventory all Windows systems and identify those running the listed versions, starting with Windows 10 1809 and Windows Server 2019.
- Verify the fixed build in the MSRC Security Update Guide and install the October 2026 cumulative update, prioritizing internet-facing and file-processing servers.
- Flag Windows 10 1809 systems without a clear support path for replacement and check Microsoft's lifecycle pages.
- Monitor for exploitation indicators and check the CISA KEV catalogue regularly until patching is complete.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Remote code execution – Windows Libarchive
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5126651, KB5126655, KB5126657, KB5126646, KB5127648, KB5126653
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Response Center: CVE-2026-69639 msrc.microsoft.com
- Strix: CVE-2026-69639 www.strix.ai
- Vulners MSCVE: MS:CVE-2026-69639 vulners.com
- Senserva: Patch Tuesday overview senserva.com
- Vulners Rapid7: CVE-2026-69639 (EPSS) vulners.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 30 Oct 2026, 18:53.
Original description (NVD)
Heap-based buffer overflow in Windows Libarchive allows an unauthorized attacker to execute code over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.