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CVE-2021-26858 is a post-authentication arbitrary file-write vulnerability in on-premises Microsoft Exchange Server 2013, 2016, and 2019. An authenticated attacker can write a file to an attacker-selected path on the Exchange server. It was one of the vulnerabilities used in the ProxyLogon attack chain and can be combined with other Exchange flaws to place server-side web shells and achieve remote code execution.
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No valid public exploits. Mallory filtered out 2 candidates 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.
64 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 post-authentication arbitrary file write vulnerability that can be used after authentication to write files to arbitrary paths on the server, often as part of the broader Exchange exploitation chain.
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.