Microsoft SharePoint Server Replay-Based Remote Code Execution
CVE-2021-27076 is a Microsoft SharePoint Server remote code execution vulnerability described in the provided content as a replay-style integrity bypass affecting SharePoint. The writeup frames the bug as an instance where authenticated or trusted data can be captured in one context and reused in another, allowing SharePoint to accept reused state in a way that does not uniquely bind the original sender’s intent, timing, or transaction context. The content explicitly identifies the issue as ZDI-21-276 / CVE-2021-27076 and discusses it as foundational to later SharePoint research. However, the specific vulnerable SharePoint function, exact request path, and precise code-level sink for CVE-2021-27076 are not provided in the supplied material.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
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.
Recent activity
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A Microsoft SharePoint vulnerability exploited in the campaign and specifically referenced in a later intrusion example.
A SharePoint vulnerability leveraged to compromise a SharePoint service running on IIS, after which attackers deployed files and used DLL sideloading for execution/persistence (including a Cobalt Strike implant).
A SharePoint replay-style deserialization vulnerability referenced as using the same session-data storage and reuse technique as the vulnerabilities discussed in the article.
A Microsoft SharePoint remote code execution vulnerability targeted by the threat actor; the report also describes post-exploitation activity in a case involving this CVE.
The version that knows your environment.
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.