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CVE-2026-20856 is an improper input validation vulnerability in Windows Server Update Service (WSUS). The flaw allows an unauthorized attacker to achieve remote code execution over a network. Available reporting indicates exploitation is associated with an adversary-in-the-middle scenario in which update-related content is modified in transit, including update metadata or update binaries, due to insufficient validation by WSUS. The vulnerability is rated with CVSS v3.1 vector AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H, indicating network reachability, no privileges required, no user interaction, and high impact across confidentiality, integrity, and availability.
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What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
No valid public exploits. Mallory filtered out 1 candidate as fakes, detection scripts, or README-only repos.
All candidate exploits were filtered out by Mallory's validation.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
4 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An improper input validation flaw in WSUS that can enable adversary-in-the-middle (AitM) tampering of update metadata/binaries to achieve remote code execution.
A remote code execution vulnerability in Windows Server Update Service (WSUS) caused by improper input validation (CWE-20), allowing an unauthenticated attacker to execute code over the network.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.