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CVE-2021-26857 is a remote code execution vulnerability in on-premises Microsoft Exchange Server that was publicly disclosed and patched in March 2021. Available reporting identifies it as an insecure deserialization flaw associated with the Exchange Unified Messaging service, specifically the UMWorkerProcess component. In the widely exploited ProxyLogon attack chain, this vulnerability was commonly used together with CVE-2021-26855 and the post-authentication file-write flaws CVE-2021-26858 and CVE-2021-27065. When reached through the broader chain, the flaw enabled arbitrary code execution on vulnerable Exchange servers, often leading to web shell deployment and follow-on compromise. Affected products include Exchange Server 2013, 2016, and 2019, with reporting also noting a defense-in-depth update for Exchange Server 2010 for this CVE.
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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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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
54 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.