Loading vulnerability…
CVE-2021-26857 is an insecure deserialization vulnerability in the Unified Messaging service of on-premises Microsoft Exchange Server 2013, 2016, and 2019. An authenticated attacker with administrator privileges can exploit unsafe deserialization to execute arbitrary code in the Exchange server context. The flaw was one component of the ProxyLogon vulnerability set and was actively exploited in conjunction with other Exchange vulnerabilities.
Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
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.
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.
61 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
One of the four vulnerabilities in the ProxyLogon exploit chain affecting Microsoft Exchange servers.
A Microsoft Exchange Unified Messaging insecure deserialization vulnerability that can enable code execution as SYSTEM when combined with administrator permission or another vulnerability.
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.
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.