Understanding and Defending Against Authentication Coercion Attacks in Windows Networks

Authentication coercion attacks have emerged as a formidable and evolving threat to enterprise networks leveraging Windows infrastructure. Despite significant advances in native Microsoft security controls, even low-privileged domain accounts can still exercise a range of techniques to force authentication attempts from high-value targets—most notably, domain controllers or sensitive application servers. This forced authentication, when successfully relayed or intercepted, often provides a gateway for lateral movement, privilege escalation, or, in worst-case scenarios, complete domain compromise.

Understanding Authentication Coercion in Modern Windows Environments​

At its core, authentication coercion is the art of making another system, typically of greater privilege, unwittingly initiate an authentication request to a server controlled by the attacker. The attacker then captures or relays this authentication, exploiting classic weaknesses in legacy protocols or misconfigured services. Modern attacks focus predominantly on credentials associated with computer accounts—entities like DOMAIN\COMPUTER$, which, while often overlooked, possess significant network rights and can be manipulated for powerful impersonation tactics such as S4U2Self or Resource-Based Constrained Delegation (RBCD).
These techniques are intimately intertwined with well-known credential relay methods, including NTLM relay and Kerberos abuse. The process typically unfolds as follows:

• Discovery: The attacker identifies suitable RPC (Remote Procedure Call) interfaces or network services on a target system (often via automated tools).
• Coercion: By invoking specific API calls or functions, the attacker tricks the target into authenticating to a network share or service of their choosing.
• Relaying or Capturing: The induced authentication (NTLM/Kerberos) is forwarded to another service or intercepted outright, potentially granting access or allowing identity impersonation.

Over the past five years, Microsoft has attempted to stem these attacks by tightening default configurations, introducing cryptographic validations, and urging organizations to migrate away from legacy protocols. Yet, as recent research and headline breaches demonstrate, older systems and incomplete deployments provide persistent openings.

Primary Techniques and Their Protocols​

The attack surface for coercion is broad because Windows supports a rich tapestry of RPC-based management and notification protocols, many of which were never designed with hostile actors in mind. Each protocol offers unique avenues for exploitation, summarized in the following table:

Method	Protocol	SMB Capable	HTTP Capable	DCERPC Capable	On Clients	On Servers
PrinterBug	MS-RPRN	Yes	Yes	Yes	Yes
PetitPotam	MS-EFSRPC	Yes	No	Yes	Yes
DFSCoerce	MS-DFSNM	Yes	No	No	No	Yes
WSPCoerce	MS-WSP	Yes	DCERPC***	Yes	No

[TD]Yes [/TD] [TD]Yes [/TD] [TD]Yes [/TD]

• Attacks over SMB/HTTP are viable on pre-Windows 11 22H2/Server 2025.
  ** MS-EFSRPC methods are broadly applicable unless specifically mitigated.
  *** Protocol capability shifts as Microsoft updates channel availability (e.g., after Server 2025, only DCERPC remains).

1. PetitPotam (MS-EFSRPC)​

PetitPotam leverages the Encrypting File System Remote Protocol to coerce outbound authentication. By abusing functions such as EfsRpcOpenFileRaw, attackers force the target—often a domain controller—to reach out to any SMB/HTTP endpoint. Tools like “Coercer” efficiently scan and exploit these vectors, automating what was previously a painstaking manual process. Independent analysis from the open-source community consistently validates the effectiveness of PetitPotam, especially in mixed environments with incomplete patching.

2. PrinterBug (MS-RPRN)​

PrinterBug exploits the Print System Remote Protocol, using print notification features to prompt credential exposure. Although Microsoft has curtailed SMB/HTTP avenues in the latest OS generations, the attack remains potent on legacy estates and where DCERPC remains exposed. Security advisories and penetration test reports confirm frequent detection of vulnerable configurations, underscoring the patch gap endemic to many organizations.

3. DFSCoerce (MS-DFSNM)​

This method abuses Distributed File System Namespace Management Protocol, available mainly on servers, to trigger SMB-based authentication. Its value is amplified in environments where default NTLM or less rigid Kerberos policies persist. Industry security blogs and proof-of-concept code confirm that DFSCoerce is particularly relevant for exploiting file infrastructure in large, distributed networks.

4. WSPCoerce (MS-WSP)​

WSPCoerce takes advantage of the Windows Search Protocol to prompt SMB authentication, especially from client workstations. Recent research has produced Python implementations that allow even non-Windows attackers to initiate these coercions cross-platform, raising the profile of the threat beyond Windows-native environments.
Proof-of-Concept: Coercing via MS-FSRVP

# Example: Forcing a server to authenticate to an attacker's SMB share
./coerce_poc.py -d "LAB.local" -u "user1" -p "Podalirius123!" 192.168.2.51 192.168.2.1

This command, as highlighted in public advisories, compels the Windows Server at 192.168.2.1 to leak its machine credentials to 192.168.2.51 under the attacker’s control.

The Risks and Enterprise Impact​

The ease of such coercion attacks—often requiring nothing more than network access and low-privilege credentials—elevates their risk profile. The attack pivots on the inherent trust models of Active Directory and legacy protocol support, often enabling:

• Silent Privilege Escalation: Gaining high privileges without triggering endpoint security alerts.
• Lateral Movement: Jumping from compromised endpoints to core infrastructure, such as domain controllers.
• Domain Escalation: Leveraging relayed credentials to impersonate users or computers, initiating secondary attacks (e.g., Kerberos delegation abuse).

More concerning is the “chaining” potential; for example, an attacker might initially coerce a domain controller, relay its credentials to a management server, and from there, achieve forest-wide compromise. Multiple independent incident response consultancies (including Mandiant, CrowdStrike, and the Microsoft Detection & Response Team) report consistent real-world cases where relay and coercion attacks played pivotal roles in ransomware delivery and data exfiltration.

Evolving Defenses: What Microsoft Got Right—and Missed​

Recognizing these dangers, Microsoft has adjusted default behaviors in the latest Windows releases:

• SMB/LDAP Signing and Channel Binding: Mandatory signing and cryptographic binding now default to “on” in new Windows 11 (24H2) and Server 2025 installations, providing strong relay attack mitigation via tamper-evident session validation.
• Deprecation of NTLM: With NTLM now officially deprecated, disabling it at the domain level closes entire categories of coercion (though real-world migration remains complex).
• Extended Protection for Authentication (EPA): EPA ensures that authentication is bound to a secure channel, neutering many “man-in-the-middle” relay attempts.

But Are Enterprises Safe?​

Unfortunately, for many organizations these advances remain aspirational rather than operational:

• Legacy and Upgraded Systems: New protections often apply only to fresh installations. Upgrades or in-place migrations retain old, less secure defaults in the name of compatibility.
• Patching Gaps: Enterprises face significant challenges in deploying patches to all endpoints, leaving a long tail of exploitable systems (especially in IT/OT convergence environments).
• Third-Party and Shadow Infrastructure: Printers, appliance devices, and legacy apps frequently re-enable Rpc or SMB services, even after hardening efforts.
• Operational Overhead: Forcing SMB signing or disabling NTLM can break older line-of-business applications and scripts, leading IT teams to balance risk against business continuity.

Security analysts warn that Microsoft’s paradigm—default security only on clean installs—may lull organizations into a false sense of confidence, while attackers simply hunt for unprotected endpoints elsewhere in the network.

Key Mitigation Strategies​

Drawing from Microsoft advisories, CERT bulletins, and leading incident response case studies, effective mitigation requires a composite, defense-in-depth approach:

1. Disable NTLM Authentication (Where Possible)​

Migrating off NTLM eliminates entire relay/coercion attack paths. For domains and apps that still require NTLM, restrict its use and monitor diligently for unusual patterns.

2. Enforce SMB/LDAP Signing and Channel Binding​

Mandate signing and binding on all servers, not just the latest Windows versions. Use Group Policy or configuration management to enforce these settings, closing the window for unauthorized relays.

3. Monitor and Restrict RPC Interfaces​

Identify exposure points using tools like BloodHound or custom RPC scanners, and restrict access to vulnerable interfaces via firewall rules and ACLs. Monitor authentication logs for anomalous outbound connections from critical assets.

4. Patch and Harden Legacy Systems​

Develop a regular patching cadence, prioritizing servers and domain controllers. Where patching isn’t possible (e.g., end-of-life products), isolate these endpoints or replace them.

5. Regularly Audit Service Accounts and Delegation Settings​

Review permissions granted via S4U2Self, RBCD, and other delegation settings, ensuring minimal privilege and adherence to the principle of least privilege.

6. User Education and Red Team Testing​

Train IT staff to recognize the telltale signs of coercion or relay in event logs, and commission regular penetration tests or red team engagement to identify exposures before attackers do.

The Arms Race: Attackers Adapt, Defenders Respond​

Authentication coercion sits at the nexus of protocol design, patch management, and enterprise sprawl. While new mitigations have raised the bar, attacker research continues apace—witness the recent publication of Python-based toolkits capable of launching coercion attacks from non-Windows devices.
Penetration testers and security researchers have repeatedly demonstrated that as long as environments contain legacy protocols, unpatched systems, or default RPC interfaces, coercion methods will remain effective. Moreover, operational realities—such as third-party vendor appliances and hybrid cloud architectures—ensure the attack surface remains wide.
Defenders, therefore, must adopt a twin-pronged philosophy:

• Proactive Hardening: Treat coercion not as an edge-case bug, but as a systemic risk requiring architectural change and relentless monitoring.
• Rapid Response: Assume breach, invest in intrusion detection around authentication infrastructure, and script automated incident response to minimize dwell time if coercion is detected.

Conclusion: Securing the Windows Enterprise Against Coercion​

The ultimate lesson is one of caution and vigilance. Authentication coercion is not an obscure, laboratory-only technique; it is repeatedly employed by ransomware operators and advanced persistent threat groups “in the wild,” as documented by both public and private sector security teams.
While Microsoft’s evolving security posture offers hope, the long tail of unpatched, misconfigured, or legacy endpoints means that vigilance, layered defense, and sustained investment in patching and monitoring are essential. Enterprise defenders must view coercion risks not only through the lens of compliance but as a daily operational reality—one that demands continuous attention as attackers refine their tools and techniques.
For organizations prioritizing cybersecurity maturity in 2025 and beyond, deep familiarity with authentication coercion—and ongoing commitment to mitigation—should be an integral part of their defense strategy. By embracing hardened defaults, scrupulous auditing, and education, security teams can turn the tide against this persistent and perilous class of threat.

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Source: GBHackers News Windows Authentication Coercion Attacks Present Major Risks to Enterprise Networks