(0Day) Microsoft Windows HTTP Proxy Privilege Escalation Vulnerability
Vulnerability Details
This vulnerability allows local attackers to escalate privileges on affected installations of Microsoft Windows. An attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability.
The specific flaw exists within the handling of authentication to HTTP proxy servers. By changing the proxy setting to point to a malicious server, an attacker can disclose NTLM responses in the context of the machine account. An attacker can leverage this vulnerability to escalate privileges to resources normally protected from the user.
Additional Details
05/07/26 – ZDI reported the vulnerability to the vendor
05/07/26 – the vendor acknowledged the receipt of the report
06/02/26 – the vendor confirmed that the issue would be fixed in September release
08/31/26 – the vendor communicated that the vulnerability did not meet the bar for security servicing
09/03/26 – ZDI notified the vendor of the intention to publish the case as a 0-day advisory
-- Mitigation: Given the nature of the vulnerability, the only salient mitigation strategy is to restrict interaction with the product
Disclosure Timeline
- 2026-05-07 - Vulnerability reported to vendor
- 2026-09-16 - Coordinated public release of advisory
- 2026-09-16 - Advisory Updated
Credit
Peter Gabaldon (https://x.com/PedroGabaldon)
