Microsoft Exchange Server Elevation of Privilege and NTLM Relay Vulnerability (CVE-2024-21410) Urgent Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTMicrosoft Exchange Server 2016 and 2019 environments where Cumulative Updates and Extended Protection are not enabled.
Unauthenticated remote attackers can perform NTLM credential relay attacks to elevate privileges, gaining administrative access to Exchange servers and compromising mailboxes.
Upgrade Exchange Server to the latest Cumulative Update (CU) and enforce the Extended Protection feature immediately.
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrade Exchange Server to the latest Cumulative Update (CU). Exchange Server 2019 CU14 and later enables Extended Protection by default.
# Check current Exchange Server version and build number in Exchange Management Shell
Get-ExchangeServer | Format-List Name, Edition, AdminDisplayVersion2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, run the official Microsoft script to manually enable Extended Protection across all Exchange virtual directories.
# Download and execute the official ExchangeExtendedProtectionManagement.ps1 script
# Note: This script may temporarily restart IIS and Exchange services.
.\ExchangeExtendedProtectionManagement.ps1
# Force enable and verify Extended Protection status
.\ExchangeExtendedProtectionManagement.ps1 -ShowDisclaimers -Force3. Log Audit & IoC Verification Commands
Audit IIS and Exchange HTTP Proxy logs to identify anomalous NTLM authentication attempts and potential relay activities.
# Search IIS logs for unusual POST requests to EWS endpoints with NTLM authentication
Get-ChildItem -Path 'C:\inetpub\logs\LogFiles\W3SVC1\' -Filter '*.log' |
Select-String -Pattern 'POST /ews/exchange.asmx' |
Select-Object -First 50Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2024-21410) is a critical Elevation of Privilege (EoP) flaw in Microsoft Exchange Server. The root cause lies in the insufficient authentication validation (CWE-287) where Exchange Server fails to properly validate Channel Binding Tokens (CBT) during NTLM authentication requests. This flaw allows an attacker to intercept and relay a victim's NTLM credentials to the Exchange Server.
2. Exploitation Mechanics & Attack Scenario
An attacker initiates the exploit by coercing a client within the network (such as an Outlook client or domain-joined machine) to authenticate against an attacker-controlled server using NTLM. Once the NTLM negotiation begins, the attacker intercepts the authentication challenge and relays it to the Exchange Server's Web Services (EWS) or OWA endpoints. If Extended Protection is disabled, the Exchange Server accepts the relayed credentials as valid, granting the attacker the session privileges of the relayed user, potentially up to Exchange Administrator.
3. Infrastructure & Business Impact
With a CVSS score of 9.8, this vulnerability is classified as Critical and is actively exploited in the wild, as confirmed by its inclusion in the CISA KEV catalog. Successful exploitation allows attackers to read sensitive corporate communications, modify mail flow rules to exfiltrate data, or leverage the compromised Exchange service account to perform lateral movement and compromise the entire Active Directory domain.
Official Vendor Advisories & References
Microsoft Exchange Server Elevation of Privilege Vulnerability
Frequently Asked SecOps Questions (CVE-2024-21410)
FAQQ1. How critical is CVE-2024-21410 and is it actively exploited in the wild?
CVE-2024-21410 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 12.7%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2024-21410?
Primary impacted vendors include microsoft across exchange_server. Scope summary: Microsoft Exchange Server 2019 (Cumulative Update 13 and prior) and Exchange Server 2016 (Cumulative Update 23 and prior) without Extended Protection enabled.
Q3. What temporary mitigations or workarounds exist for CVE-2024-21410 before patching?
[Mitigation] Upgrade Exchange Server to the latest Cumulative Update (CU) and enforce the Extended Protection feature immediately. Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2024-21410
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