In May 2022, Microsoft patched a critical vulnerability identified as CVE-2022-29137 that affects the Windows LDAP (Lightweight Directory Access Protocol) service. This is a remote code execution (RCE) issue that could let an attacker run arbitrary code on vulnerable systems—if properly exploited. While there are other LDAP vulnerabilities in the same year (CVE-2022-22012, CVE-2022-22013, CVE-2022-22014, CVE-2022-29128, CVE-2022-29129, CVE-2022-29130, CVE-2022-29131, CVE-2022-29139, and CVE-2022-29141), CVE-2022-29137 stands out for its unique exploitation vector.

Let’s unpack what makes this vulnerability dangerous, how it can be exploited (with simple code), and what you should do.

What is CVE-2022-29137?

CVE-2022-29137 is a bug found in the Windows LDAP service, specifically in how the service parses certain LDAP requests. If attackers manage to send specially crafted packets to a server that listens for LDAP traffic (usually on port 389 or 636 for LDAPS), they could exploit this flaw to execute malicious code with SYSTEM privileges.

Severity: High (CVSS 8.8)

- Affected versions: Windows Server 2012, 2016, 2019, 2022, and Windows 10/11 with AD DS (Active Directory Domain Services) role installed.

Microsoft Advisory:  
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2022-29137

How Does The Exploit Work?

LDAP is a protocol Microsoft relies on for Active Directory (AD) operations. The vulnerability arises due to improper inputs handling, leading to out-of-bounds memory writes (or something similar under the hood), which enables remote code execution.

For exploitation, the intruder needs network-level access to the LDAP service, which in many enterprises is exposed within the organization's internal network.

Scenario:  
An attacker, after gaining a foothold inside a corporate network, could send crafted LDAP packets to the domain controller. If successful, this would allow malware installation, lateral movement, or privilege escalation.

Technical Details

While Microsoft didn’t publish full technical details, researchers have reverse engineered public patches and dissected the updates. The issue seems related to improper handling of input data in LDAP requests, specifically with BER (Basic Encoding Rules) encoded data, a format LDAP uses.

Here’s a simplified code snippet (Python) that demonstrates the basic concept—sending a malformed LDAP request to a target server:

import socket

# IP Address of the LDAP server (Domain Controller)
target_ip = "192.168.1.100"
ldap_port = 389

# This is a generic BER-encoded malformed LDAP packet
malformed_packet = bytes([
    x30, x84, xFF, xFF, xFF, xFF,    # Message sequence header with large length
    # ... more crafted fields ...
])

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
try:
    s.connect((target_ip, ldap_port))
    s.send(malformed_packet)
    print("Malformed packet sent!")
except Exception as e:
    print(f"Failed to send packet: {e}")
finally:
    s.close()

Note:
The payload above is a placeholder. The real attack would require precise construction of the packet format, which is not released for ethical reasons. Still, this shows the general idea of sending raw data to exploit LDAP.

Detection and Mitigation

Detection:

Use network monitoring tools to catch malformed or abnormally large LDAP packets.

Mitigation:

Microsoft’s May 2022 Patch Tuesday rolled out fixes. See:

CVE-2022-29137 Microsoft Update Guide

Use firewalls to limit exposure of LDAP services to necessary segments.

Workarounds:

Additional References

- Microsoft advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2022-29137

Security researchers’ blog:

The DFIR Report - LDAP Vulnerabilities

General BER parsing bug discussions:

OWASP LDAP Injection

Conclusion

CVE-2022-29137 is a powerful reminder that LDAP—one of the backbone protocols in Windows environments—must be secured, monitored, and patched urgently. Attackers can abuse a single memory handling flaw in LDAP to gain domain-level control in target networks. Businesses of all sizes should patch this ASAP and review LDAP security posture in their organization.

Timeline

Published on: 05/10/2022 21:15:00 UTC
Last modified on: 05/23/2022 17:29:00 UTC