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Hackers Actively Searching for Unpatched Microsoft Exchange Servers
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Nearly 22,000 Microsoft Exchange servers remain exposed to critical security flaw (CVE-2026-62911)
About 22,000 Microsoft Exchange servers remain unpatched against critical auth bypass CVE-2026-62911 as a working exploit circulates online.
CVE-2026-62911 is a critical authentication bypass by capture-replay in Microsoft Exchange Server that allows an authorized attacker to elevate privileges over the network, with a CVSS score of 8.0. Microsoft patched the flaw on August 11, 2026, but Shadowserver Foundation scans show roughly 22,000 servers unpatched, with the US (6,200) and Germany (5,100) leading; BSI reports 85% of on-premises Exchange servers in Germany are still vulnerable. The Netherlands' NCSC-NL flagged that a working exploit is circulating, and Exchange 2016/2019 require the Extended Security Updates program for fixes.
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Threat Brief: OWASSRF Vulnerability Exploitation
Unit 42 details active exploitation of Exchange SSRF flaws CVE-2022-41080/CVE-2022-41082 via the OWASSRF method, deploying the SilverArrow PowerShell backdoor.
Unit 42 documents OWASSRF, an exploit chain combining CVE-2022-41080 and CVE-2022-41082 to achieve remote code execution on Microsoft Exchange via Outlook Web Access, bypassing Microsoft's ProxyNotShell mitigations. Active exploitation was observed in late November and early December 2022, affecting at least eight organizations. Attackers authenticated to Exchange, then executed a PowerShell backdoor tracked as SilverArrow to create admin accounts, install AnyDesk, tunnel RDP via PuTTY Link, and dump LSASS memory for credential theft. Exploitation is isolated rather than mass-scale because authentication is required.
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Microsoft Exchange Vulnerability CVE-2026-62911: What Administrators Should Do and How Zscaler Can Help
High-severity authentication bypass CVE-2026-62911 in Exchange Server has public exploit code; about 22,000 servers remain unpatched and internet-exposed.
Microsoft's August 2026 Patch Tuesday fixed CVE-2026-62911 (CVSS 8.0), an authentication bypass affecting Exchange Server 2016, 2019 and Subscription Edition. Successful exploitation lets an attacker with basic privileges take over all mailboxes on the targeted server, including reading and sending email and downloading attachments. As of September 1, Shadowserver identified roughly 22,000 unpatched, internet-exposed Exchange servers, including about 6,200 in the US and 5,100 in Germany. NCSC-NL confirmed working exploit code is publicly available, while CISA has not yet reported exploitation in the wild.
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U.S. CISA adds Dahua IP Camera, Linux Kernel and Microsoft Exchange Server bugs to its Known Exploited Vulnerabilities catalog
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The September 2026 Security Update Review
ZDI's September 2026 Microsoft update review lists two already-exploited Windows EoP zero-days and dozens of critical RCEs across Office, SQL Server, and Windows services.
The review catalogs Microsoft's September 2026 fixes, marking CVE-2026-85880 (Windows ALPC) and CVE-2026-81963 (Windows Update Stack) as already exploited elevation-of-privilege issues. It also lists critical RCE flaws in Office, Word, Excel, PowerPoint, Outlook, SQL Server, Windows DNS, DHCP and Failover Cluster, plus graphics component RCEs. Azure-side fixes include Entra ID, Copilot Studio, Azure AI Language and Azure AD B2C elevation-of-privilege flaws.
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