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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.

Zscaler ThreatLabz · 12d agoVulnerabilityCVE-2026-629112

Related CVEs

  • CVE-2026-629118.01%
    Capture-Replay Authentication Bypass in Microsoft Exchange Server
    Microsoft Exchange Server contains an authentication bypass flaw (CWE-294) in which captured authentication material can be replayed, allowing an authorized attacker to elevate privileges over a network. Per the CVSS vector, the attack is network-based with low complexity but requires the attacker to already hold low privileges and some user interaction, and success yields high impact on confidentiality, integrity, and availability. Affected products include on-premises Exchange Server and Exchange Server Subscription Edition, though specific vulnerable version ranges are not specified in the available data. Public scans indicate nearly 22,000 Exchange servers remain exposed to the flaw following the August 2026 Patch Tuesday fixes. No in-the-wild exploitation, public proof-of-concept, or KEV listing is known; the bug was demonstrated at Pwn2Own (ZDI-26-534) and carries an EPSS estimate of 1.3% probability of exploitation within 30 days.
    · microsoft exchange server · microsoft exchange server subscription editionlarge

Appears with

organization CISA 1organization NCSC-NL 1organization Shadowserver 1product Exchange Server 1product Exchange Server 2019 1product Exchange Server Subscription Edition 1vendor Microsoft 1vendor Zscaler 1
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