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CVE-2021-26857 is a remote code execution vulnerability in the Unified Messaging service of on-premises Microsoft Exchange Server. The flaw is an insecure deserialization issue in which untrusted, user-controllable data is deserialized by the Unified Messaging component. Successful exploitation allows arbitrary code execution in the context of the Exchange server, and reported exploitation resulted in code running as NT AUTHORITY\SYSTEM. The vulnerability was one of the March 2021 Exchange flaws commonly associated with the ProxyLogon intrusion chain and affected on-premises Exchange deployments rather than Exchange Online or Microsoft 365.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos (2 hidden).
This repository contains a Python exploit (exploit.py) for the ProxyLogon vulnerability (CVE-2021-26857) in Microsoft Exchange Server. The exploit targets unpatched Exchange servers accessible over HTTPS and requires a valid email address on the target system. The script performs a series of HTTP requests to the Exchange Control Panel (ECP) endpoints to authenticate, escalate privileges, and ultimately write a JScript/ASP.NET web shell to the server's OWA authentication directory. The web shell allows remote code execution by sending commands via HTTP POST requests. The repository includes a README with usage instructions and a single exploit script. The exploit is operational and provides a working web shell payload, but is not part of a larger framework.
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34 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A specific Microsoft Exchange Server vulnerability that is part of the ProxyLogon exploit chain used by SHADOW-EARTH-053 for initial compromise.
A Microsoft Exchange Server vulnerability that is part of the ProxyLogon exploit chain used to compromise unpatched internet-facing Exchange servers for espionage operations.
A Microsoft Exchange Server vulnerability that is part of the ProxyLogon exploit chain used by the threat group for initial access into unpatched Exchange environments.
A Microsoft Exchange Server vulnerability referenced as part of the ProxyLogon exploit chain used to achieve remote code execution.
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.