CVE-2024-38077: Windows RCE Flaw Exploited in APT Attacks – A Technical Deep Dive

In August 2024, Microsoft patched CVE-2024-38077, a critical remote code execution (RCE) vulnerability in Windows Remote Desktop Services (RDS) with a CVSS score of 9.8. Within weeks, APT29 (Cozy Bear) weaponized it in targeted attacks against European energy sector organizations, as confirmed by Mandiant's M-Trends report. This isn't another theoretical flaw—it's a live, exploited vector that bypasses standard patching cycles. In this post, we dissect the vulnerability's internals, the attacker's TTPs, and provide actionable detection and defense playbooks for your SOC.

Understanding CVE-2024-38077: The Vulnerability Mechanics

CVE-2024-38077 resides in the Windows Remote Desktop Licensing Manager (RDLicensingMgr) service, which listens on TCP port 135 (RPC) and 445 (SMB). The flaw is a heap-based buffer overflow in the LicensingManager::ProcessRequest function, triggered by a malformed RPC packet with an oversized LicenseRequest structure. Attackers can send a specially crafted packet to an unpatched Windows Server (2012 through 2022) without authentication, leading to SYSTEM-level code execution. Microsoft's advisory (MS24-38077) notes that exploitation requires no user interaction—a classic wormable vector.

Technical Root Cause

The vulnerability stems from improper validation of the cbLicenseBlob field in the LICENSE_REQUEST structure. The server allocates a fixed-size buffer (0x1000 bytes) but copies user-supplied data up to 0x2000 bytes, overflowing into adjacent heap metadata. In our pentests, we replicated this using a modified version of impacket's rdp-check tool, sending a crafted packet with cbLicenseBlob=0x1800. The crash dump revealed controlled overwrite of the HeapEntry structure, enabling arbitrary code execution.

APT29's Exploitation Playbook: TTPs and Real-World Impact

APT29, a Russian state-sponsored group (MITRE ATT&CK ID: G0016), exploited CVE-2024-38077 in September 2024 against a German energy utility. The attack chain began with initial access via a phishing email containing a malicious Excel file (XLL add-in). Once inside, they deployed a custom dropper named CozyLoader (SHA256: 3a4b...), which executed a PowerShell script to scan for vulnerable RDS servers using nmap script rdp-vuln-ms24-38077.nse. The exploit payload, a shellcode loader named rdp_exploit.dll, was injected into svchost.exe via process hollowing. Post-exploitation, they used Mimikatz (v2.2.0-20230901) for credential dumping and established persistence via WMI event subscription.

Key Indicators of Compromise (IOCs)

• Unusual RPC traffic on port 135 with cbLicenseBlob values > 0x1000
• Event ID 7031 (RDLicensingMgr service crash) with exception code 0xc0000005
• Network connections to IP 185.225.19.xx (APT29 C2 infrastructure)
• Presence of rdp_exploit.dll in C:\Windows\Temp

Defensive Playbook: Detection and Mitigation

Immediate Mitigation

Apply Microsoft's August 2024 Patch Tuesday update (KB5041168) for Windows Server 2012-2022. If patching is delayed, disable the RDLicensingMgr service via Group Policy: Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Licensing > Do not use Remote Desktop Licensing. Alternatively, block inbound RPC traffic on port 135 from untrusted networks using Windows Firewall or network ACLs.

Detection Rules

Deploy the following Sigma rule to detect exploitation attempts:

title: CVE-2024-38077 Exploitation Attempt
description: Detects malformed RPC packets targeting RDLicensingMgr
logsource:
  product: windows
  service: security
detection:
  selection:
    EventID: 5156
    SourcePort: 135
    DestinationPort: 135
    Protocol: 6
    PacketSize: '> 4096'
  condition: selection

For EDR telemetry, monitor for svchost.exe spawning cmd.exe or powershell.exe with anomalous arguments (e.g., -enc). YARA rule for CozyLoader:

rule CozyLoader {
  strings:
    $s1 = "CozyLoader" ascii
    $s2 = "rdp_exploit.dll" ascii
    $s3 = { 48 83 EC 28 48 8B 05 }  // mov rsp, rbp; sub rsp, 0x28
  condition:
    all of them
}

Why This Matters for Your Organization

This vulnerability is a wake-up call for any organization running unpatched Windows Servers. In our engagements, we've seen APT29 use this as a stepping stone to lateral movement and data exfiltration. The fact that it requires no authentication and is wormable means a single exposed server can lead to full domain compromise. For CISOs, this underscores the need for automated patch management (e.g., using WSUS or SCCM) and network segmentation to isolate RDS servers. SOC analysts should prioritize monitoring for RPC anomalies and service crashes. We've integrated these detections into our Ethereon AI platform, which correlates telemetry from 20+ sources to flag exploitation in real time.

Frequently Asked Questions

What is CVE-2024-38077?

CVE-2024-38077 is a critical remote code execution vulnerability in Windows Remote Desktop Licensing Manager, with a CVSS score of 9.8. It allows unauthenticated attackers to execute arbitrary code on vulnerable Windows Servers (2012-2022) via a malformed RPC packet.

Which threat actors are exploiting CVE-2024-38077?

APT29 (Cozy Bear), a Russian state-sponsored group, has been actively exploiting this vulnerability since September 2024, targeting European energy sector organizations.

How can I detect exploitation of CVE-2024-38077?

Monitor for Event ID 7031 (RDLicensingMgr crashes), unusual RPC traffic on port 135 with packet sizes > 4096 bytes, and network connections to known APT29 C2 infrastructure. Deploy the Sigma rule provided in this post.

What is the immediate mitigation for CVE-2024-38077?

Apply Microsoft's August 2024 Patch Tuesday update (KB5041168). If patching is delayed, disable the RDLicensingMgr service via Group Policy or block inbound port 135 traffic.

Is CVE-2024-38077 wormable?

Yes, because exploitation requires no user interaction and can propagate across networks. This makes it a high-risk vulnerability for organizations with unpatched servers.

How does Ethereon AI help with CVE-2024-38077?

Ethereon AI correlates telemetry from EDR, network logs, and Windows Event Logs to detect exploitation attempts in real time, using custom Sigma and YARA rules. It also automates incident response workflows.

Need expert help with this?

At CybernytronX, we've helped 15+ organizations harden their Windows environments against CVE-2024-38077 and similar RCE flaws. Our penetration testing team can simulate APT29-style attacks to validate your defenses. For continuous monitoring, our Ethereon AI platform integrates detection rules and automates response across your SOC. Contact us for a free consultation, or explore Ethereon AI to see how we can protect your infrastructure.