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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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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U.S. CISA adds Dahua IP Camera, Linux Kernel and Microsoft Exchange Server bugs to its Known Exploited Vulnerabilities catalog
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ZDI-26-538: (Pwn2Own) Microsoft Exchange Improper Authorization Privilege Escalation Vulnerability
ZDI discloses a Pwn2Own Microsoft Exchange privilege-escalation flaw (CVE-2026-62911, CVSS 8.8) where the required authentication can be bypassed.
ZDI advisory ZDI-26-538 describes CVE-2026-62911, an improper authorization vulnerability in Microsoft Exchange rated CVSS 8.8. Remote attackers can escalate privileges, and while authentication is nominally required, the existing authentication mechanism can be bypassed. The vulnerability was demonstrated at Pwn2Own.
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ZDI-26-535: (Pwn2Own) Microsoft Exchange External Control of File Path Remote Code Execution Vulnerability
ZDI advisory discloses Microsoft Exchange remote code execution flaw (CVE-2026-62911, CVSS 7.2) with bypassable authentication.
ZDI advisory ZDI-26-535 describes an external control of file path vulnerability in Microsoft Exchange, tracked as CVE-2026-62911 with a CVSS score of 7.2. Remote attackers can execute arbitrary code on affected installations. Although authentication is required, the existing authentication mechanism can be bypassed.
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ZDI-26-534: (Pwn2Own) Microsoft Exchange Capture-Replay Authentication Bypass Vulnerability
Pwn2Own-demoed CVE-2026-62911 capture-replay authentication bypass in Microsoft Exchange allows unauthenticated remote attacks, CVSS 8.1.
ZDI-26-534 describes a capture-replay authentication bypass vulnerability in Microsoft Exchange, demonstrated at Pwn2Own, allowing remote attackers to bypass authentication without credentials. ZDI assigned a CVSS score of 8.1, and the flaw is tracked as CVE-2026-62911. Exchange servers are widely deployed enterprise mail infrastructure.
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September 2026 Microsoft Patch Tuesday, (Tue, Sep 8th)
Microsoft's September 2026 Patch Tuesday fixes a record 973 vulnerabilities, including 113 critical and two Windows privilege-escalation flaws already exploited in the wild.
Microsoft patched 973 vulnerabilities this month, its largest Patch Tuesday ever and far above the previous record of 664 set in July 2026, with 113 rated critical. Two Important elevation-of-privilege flaws (CVSS 7.8) are confirmed exploited in the wild: CVE-2026-81963 in the Windows Update Stack (improper link resolution, affects Windows 11 and Server 2025) and CVE-2026-85880 in Windows ALPC (heap-based buffer overflow allowing sandbox escape to SYSTEM, affects Windows 10 and Server 2012-2022). Critical unauthenticated RCEs (CVSS 9.8) were also fixed in Skype for Business Server (CVE-2026-66302), Windows Message Queuing (CVE-2026-69579), and Windows RRAS (CVE-2026-69590). SANS urges prioritizing the two exploited EoP fixes, then patching exposed MSMQ, RRAS, and Skype for Business deployments.
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