EUVD-2026-43815
GHSA-pp8g-rw5h-xf5x
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local EoP requiring an existing low-privilege session (AV:L, PR:L), no user interaction and low complexity (UI:N, AC:L), yielding full SYSTEM-level C/I/A impact on the host.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Integer overflow or wraparound in Windows Web Proxy Auto-Discovery Protocol (WPAD) allows an authorized attacker to elevate privileges locally.
AnalysisAI
Local privilege escalation in the Windows Web Proxy Auto-Discovery Protocol (WPAD) component lets an already-authenticated local user run code with SYSTEM-level rights by triggering an integer overflow (CWE-190). The flaw affects a broad range of Windows client and server builds, from Windows 10 1809 through Windows 11 26H1 and Windows Server 2019 through 2025. There is no public exploit identified at time of analysis and it is not listed in CISA KEV, but the low attack complexity and high triad impact make it a meaningful patch-tier issue.
Technical ContextAI
WPAD is the Windows mechanism that lets clients automatically locate a proxy configuration (a PAC file) via DHCP/DNS discovery, handled by the operating system's proxy auto-config service. The root cause is CWE-190 (integer overflow or wraparound): a length or size value processed by the WPAD code path wraps around, leading to an undersized allocation or out-of-bounds memory operation - consistent with the associated 'Buffer Overflow' tag. Successful corruption of memory in a privileged Windows service context enables the attacker to hijack execution flow and gain elevated privileges. The CPE data confirms this is a core OS component present across Windows 10 (1809, 21H2, 22H2), Windows 11 (24H2, 25H2, 26H1), and Windows Server (2019, 2022, 2025), including Server Core installations.
RemediationAI
Apply the Microsoft security update for CVE-2026-49800 via Windows Update or WSUS; the vendor-released patch is available and the exact fixed KB/build for each affected SKU is listed at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-49800. Because exploitation is local and requires an existing low-privilege session, interim compensating controls include disabling WPAD/automatic proxy discovery where it is not needed (via the 'Automatically detect settings' setting or the WinHTTP/WPAD service and the relevant DisableWpad registry policy) and tightening which users can obtain interactive or service logon on the host - with the trade-off that disabling WPAD breaks environments that legitimately rely on auto-proxy configuration. Standard EoP hardening (least-privilege accounts, restricting local logon rights) reduces the pool of attackers who can reach the vulnerable code path until patching completes.
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Same weakness CWE-190 – Integer Overflow or Wraparound
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today