Active exploitation begins after PoC release
Threat actors have initiated active exploitation of CVE-2026-55040, a critical authentication bypass in Microsoft SharePoint Server, immediately following the public release of proof-of-concept code. The vulnerability, which carries a CVSS score of 9.1, was addressed by Microsoft during its July 2026 Patch Tuesday cycle but is now being leveraged in the wild to circumvent security controls and gain unauthorized access to sensitive data.
The flaw: Critical authentication bypass
CVE-2026-55040 is a critical security feature bypass in Microsoft SharePoint Server, rooted in weak authentication mechanisms that allow attackers to circumvent standard access controls. The flaw carries a CVSS score of 9.1, reflecting both severe potential impact and high exploitability. This vulnerability was remediated by Microsoft during its July 2026 Patch Tuesday cycle.
Patching status and exposure window
Microsoft released the fix for CVE-2026-55040 during its July 2026 Patch Tuesday cycle, closing the authentication bypass in SharePoint Server. However, the rapid transition from public proof-of-concept release to active exploitation has created a critical exposure window for organizations that have not yet deployed these specific updates. Any environment still running unpatched versions of the server is currently vulnerable to unauthorized access and data compromise, making immediate remediation essential to mitigate ongoing threat activity.
Key points
- CVE-2026-55040 is a critical security feature bypass in Microsoft SharePoint with a CVSS score of 9.1.
- The vulnerability stems from weak authentication mechanisms that allow unauthorized access to the system.
- Active exploitation has been observed in the wild following the public release of proof-of-concept code.
- Microsoft patched this flaw as part of its July 2026 Patch Tuesday updates.
- Organizations are urged to apply patches immediately and monitor for signs of unauthorized access.
Further reading & sources
- AmnesiaStealer Gives Attackers Live Control of Victims’ macOS Browsers — Security Affairs
- SharePoint auth bypass exploited
- Attackers Exploit SharePoint Authentication Bypass After Public PoC Release
- US Authorizes Private Cyber Firms to Hack Transnational Criminal Networks
- Adobe Commerce CVE-2026-71362 Comes Under Attack Shortly After Public Disclosure
- U.S. CISA adds Metabase, Windows, and Cisco Secure Firewall flaws to its Known Exploited Vulnerabilities catalog
- SharePoint CVE-2026-55040 Comes Under Attack Following Public Exploit
- Chess.com Leak Exposes 7.3 Million Users — Evidence Points to Scraping
- BianLian Ransomware: Shadow Data Extortion Group - Threat Actors
- Hackers leverage new Microsoft SharePoint exploit in attacks
- Resecurity | From Web Request to Domain Compromise: Understanding the July 2026 SharePoint Attacks
- Zero Day Initiative — The July 2026 Security Update Review
- SharePoint Server vulnerabilities: How to find impacted assets