What We Know
The reported attack chain targets Microsoft SharePoint Server by combining CVE-2026-55040, an authentication-bypass vulnerability, with CVE-2026-63520, a remote-code-execution vulnerability.2Backed by 2 sourcesdecipher.sccensys.com Security researchers have developed or released proof-of-concept exploit code for the chain, and reporting says hackers are targeting SharePoint systems with it.2Backed by 2 sourcesBleepingComputercisovoice.com
The chain is described as allowing unauthenticated attackers to execute code on vulnerable servers, while CVE-2026-55040 is listed as a known exploited vulnerability.1Backed by 1 sourcescisovoice.com Rapid7, VulnCheck and other security organizations have published technical analyses or advisories focused on the two vulnerabilities and their use together.3Backed by 3 sourcesrapid7.comvulncheck.comcensys.com
Tenable characterizes cve 2026 55040 as a network exploitable sharepoint authentication weakness and lists it as a known exploited vulnerability1Context from one sourcetenable.com
Source Comparison
Aligned reportingCorroborates
- BleepingComputer↗Its headline reports hackers targeting a SharePoint RCE chain involving a PoC exploit.
- decipher.sc↗The headline identifies an unauthenticated RCE chain involving both cited SharePoint vulnerabilities.
- rapid7.com↗Rapid7 provides a technical analysis specifically focused on the Microsoft SharePoint RCE vulnerability CVE-2026-63520.
- vulncheck.com↗VulnCheck reports shipping an exploit that chains the two recently disclosed SharePoint CVEs, and its post is a focused technical analysis of that chain.
- censys.com↗Censys published an advisory explicitly covering the SharePoint authentication-bypass and RCE vulnerabilities together.
- cisovoice.com↗Its headline directly describes the chain as enabling unauthenticated attackers to execute code on vulnerable SharePoint servers.