Authentication Bypass in Microsoft Exchange Server by Microsoft
CVE-2026-62911

8HIGH

Key Information:

Vendor

Microsoft
Status
Microsoft Exchange Server 2016 Cumulative Update 23
Microsoft Exchange Server 2019 Cumulative Update 14
Microsoft Exchange Server 2019 Cumulative Update 15
Microsoft Exchange Server Subscription Edition Rtm
Vendor
CVE Published:
11 August 2026

Badges

📈 Trended📈 Score: 4,380💰 Ransomware👾 Exploit Exists🟡 Public PoC📰 News Worthy

What is CVE-2026-62911?

CVE-2026-62911 is a vulnerability identified in Microsoft Exchange Server that facilitates an authentication bypass via a capture-replay attack. Microsoft Exchange Server is a widely used email and collaboration platform that enables organizations to manage emails, calendars, and contacts efficiently. This specific vulnerability allows an authorized attacker to gain elevated privileges within the network, which can lead to unauthorized access to sensitive information and functions. Given the integral role of Microsoft Exchange in organizational communication, the exploitation of this vulnerability could compromise the confidentiality, integrity, and availability of critical business data.

Potential impact of CVE-2026-62911

  1. Unauthorized Access: The authentication bypass could allow attackers to gain unauthorized access to user accounts, enabling them to manipulate data, send emails, or exfiltrate sensitive information without detection.

  2. Privilege Escalation: Attackers can leverage the vulnerability to escalate their privileges within the network, potentially gaining control over critical systems and resources, which can lead to significant security breaches.

  3. Data Compromise: The exploitation of this vulnerability poses a risk of data breaches, including exposure of corporate emails and confidential information, leading to potential financial loss, reputational damage, and regulatory consequences for organizations.

Affected Version(s)

Microsoft Exchange Server 2016 Cumulative Update 23 x64-based Systems 15.01.0.0 < 15.01.2507.072

Microsoft Exchange Server 2019 Cumulative Update 14 x64-based Systems 15.02.0.0 < 15.02.1544.044

Microsoft Exchange Server 2019 Cumulative Update 15 x64-based Systems 15.02.0.0 < 15.02.1748.049

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-62911
Created by hypnguyen1209

News Articles

favicon imageHelp Net Security

Week in review: Claude accounts compromised through infostealer, Patch Tuesday forecast - Help Net Security

Here’s an overview of some of last week’s most interesting news, articles, interviews and videos: Anthropic locks out Claude users after infostealers

1 day ago

favicon imageEmit Post

Critical Exchange bypass flaw leaves 22,000 servers open

CVE-2026-62911, a critical Exchange authentication-bypass flaw, still exposes ~22,000 servers as a working exploit circulates despite an August patch.

2 days ago

favicon imageTechtimes

Microsoft Exchange Exploit Requires No Password: 22,000 Servers Exposed, ESU Ends October

CVE-2026-62911 Exchange Server flaw lets attackers seize all mailboxes with no password: nearly 22,000 servers remain unpatched worldwide three weeks after Microsoft’s August fix shipped, 85 percent

5 days ago

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE...
vendor-advisorypatch

CVSS V3.1

Score:
8
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
Required
Scope:
Unchanged

Timeline

  • 💰

    Used in Ransomware

  • 📰

    First article discovered by Cybersecuritynews

  • 📈

    Vulnerability started trending

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

.