CVE-2026-20829 is an out-of-bounds read vulnerability classified under CWE-125 affecting the Trusted Platform Module (TPM) implementation in Microsoft Windows 10 Version 1809 (build 17763.0). The TPM is a hardware-based security feature designed to securely store cryptographic keys and perform platform integrity measurements. This vulnerability allows an attacker with authorized local access and low privileges to read memory outside the intended buffer boundaries within the TPM software stack. Such an out-of-bounds read can lead to disclosure of sensitive information stored in adjacent memory regions, potentially including cryptographic keys or other security-sensitive data. The vulnerability does not require user interaction and does not impact system integrity or availability, focusing solely on confidentiality breaches. The CVSS v3.1 score of 5.5 reflects a medium severity, with an attack vector limited to local access (AV:L), low attack complexity (AC:L), and privileges required (PR:L). No known exploits have been reported in the wild, and no official patches have been released at the time of publication. The vulnerability was reserved in December 2025 and published in January 2026, indicating recent discovery. The lack of patches necessitates immediate mitigation strategies to protect affected systems. Given the TPM's role in securing cryptographic operations and platform integrity, this vulnerability could undermine trust in security mechanisms if exploited. Organizations running Windows 10 Version 1809 with TPM enabled should assess exposure and plan upgrades or mitigations accordingly.

For European organizations, the primary impact of CVE-2026-20829 is the potential unauthorized disclosure of sensitive information stored or processed by the TPM on affected Windows 10 Version 1809 systems. This could include cryptographic keys, credentials, or other security-critical data, potentially enabling further attacks or data breaches. The vulnerability requires local access with some privileges, so insider threats or attackers who have gained limited local footholds pose the main risk. Confidentiality breaches could affect sectors handling sensitive personal data, intellectual property, or critical infrastructure controls. Since TPM is widely used for device attestation and secure boot, exploitation could undermine trust in endpoint security, complicating compliance with European data protection regulations such as GDPR. The lack of impact on integrity and availability reduces the risk of system disruption but does not eliminate the threat to data confidentiality. Organizations relying on legacy Windows 10 1809 deployments, especially in regulated industries or government, face higher exposure. The absence of known exploits in the wild provides a window for proactive mitigation before active exploitation occurs.

To mitigate CVE-2026-20829, European organizations should prioritize upgrading affected systems from Windows 10 Version 1809 to a supported and patched Windows version where this vulnerability is addressed. If immediate upgrades are not feasible, restrict local access to affected devices by enforcing strict access controls, limiting administrative privileges, and monitoring for unauthorized local logins. Implement endpoint detection and response (EDR) solutions to detect anomalous local activity that could indicate exploitation attempts. Disable or restrict TPM usage on non-critical systems where possible, or configure TPM policies to minimize exposure. Regularly audit and inventory systems to identify those running the vulnerable Windows 10 build with TPM enabled. Educate IT staff and users about the risks of local privilege escalation and enforce strong physical security controls to prevent unauthorized device access. Stay updated with Microsoft advisories for patches or workarounds and apply them promptly once available. Consider network segmentation to isolate legacy systems and reduce attack surface. Finally, integrate this vulnerability into risk assessments and incident response plans to ensure readiness.