A critical Windows-specific Server-Side Request Forgery (SSRF) vulnerability in Apache HTTP Server has been identified, designated CVE-2025-59775, which could allow attackers to force the server to connect to malicious UNC paths and potentially leak NTLM authentication credentials. This vulnerability specifically affects Apache HTTP Server installations on Windows operating systems and represents a significant security risk for organizations running web servers on Microsoft platforms. The flaw enables attackers to exploit the server's trust relationships and potentially gain unauthorized access to sensitive network resources through credential theft.

Understanding CVE-2025-59775: The Technical Details

The vulnerability exists in how Apache HTTP Server on Windows handles certain request configurations that can be manipulated to force the server to make outbound connections to attacker-controlled Universal Naming Convention (UNC) paths. UNC paths are used in Windows networks to specify the location of resources such as shared files or printers, typically following the format \\server\share. When Apache is tricked into connecting to a malicious UNC share, it may automatically attempt to authenticate using the server's Windows credentials, potentially leaking NTLM (NT LAN Manager) hashes to the attacker.

According to security researchers, the vulnerability stems from improper validation of user-supplied input that can influence the server's connection behavior. Attackers can craft specially designed HTTP requests that manipulate the server into initiating SMB (Server Message Block) connections to systems under their control. This SSRF capability is particularly dangerous because it bypasses network perimeter defenses by originating from the trusted web server itself, potentially allowing attackers to reach internal systems that would normally be inaccessible from external networks.

The NTLM Credential Leakage Mechanism

NTLM authentication is a challenge-response protocol used in Windows environments for network authentication. When a Windows system attempts to access a network resource requiring authentication, it engages in an NTLM handshake that can reveal information about the system's credentials. In the context of CVE-2025-59775, when Apache HTTP Server on Windows is forced to connect to an attacker-controlled SMB share, it may automatically attempt to authenticate, sending NTLM negotiation messages that contain valuable information for credential attacks.

Security analysis indicates that leaked NTLM hashes can be leveraged in various attack scenarios:

  • Pass-the-Hash Attacks: Attackers can use captured NTLM hashes to authenticate to other systems without needing to crack the actual passwords
  • Relay Attacks: NTLM authentication attempts can be relayed to other systems, potentially granting unauthorized access
  • Credential Cracking: With sufficient computing resources, attackers may attempt to crack the hashes to obtain plaintext passwords
  • Lateral Movement: Compromised credentials can facilitate movement through network segments

The severity of this vulnerability is amplified by the fact that web servers often run with elevated privileges or service accounts that have access to multiple systems within an organization's network infrastructure.

Affected Versions and Patch Requirements

The vulnerability affects multiple versions of Apache HTTP Server running on Windows operating systems. According to the Apache Software Foundation's security advisory, the following versions are impacted:

  • Apache HTTP Server 2.4.0 through 2.4.65 on Windows platforms
  • Earlier 2.4.x versions running on Windows systems

Notably, installations on Linux, Unix, or other non-Windows platforms are not affected by this specific vulnerability, as the issue relates specifically to Windows UNC path handling and NTLM authentication mechanisms unique to Microsoft environments.

The Apache Software Foundation has released version 2.4.66 to address this vulnerability. Organizations running affected versions must upgrade to Apache HTTP Server 2.4.66 or later to mitigate the security risk. The patch includes proper validation and sanitization of input that could influence outbound connections, preventing malicious manipulation of UNC path requests.

Real-World Impact and Attack Scenarios

In practical terms, CVE-2025-59775 could enable several concerning attack vectors against organizations running Apache on Windows servers:

External to Internal Network Penetration: Attackers outside the network perimeter could potentially access internal systems by forcing the web server to connect to internal UNC paths, effectively using the web server as a proxy to bypass firewall restrictions.

Credential Harvesting Campaigns: Malicious actors could set up SMB servers designed to capture NTLM authentication attempts, collecting credential hashes from multiple organizations over time.

Supply Chain Attacks: If the vulnerable Apache server is part of a development or deployment pipeline, compromised credentials could lead to further infiltration of software development processes.

Cloud Environment Risks: Windows servers running Apache in cloud environments could be targeted, with potential cross-tenant implications depending on the cloud provider's security model.

Security researchers emphasize that while the vulnerability requires specific conditions to exploit successfully, the potential impact justifies immediate attention, particularly for organizations with sensitive data or critical infrastructure dependencies.

Mitigation Strategies Beyond Patching

While upgrading to Apache HTTP Server 2.4.66 is the primary solution, organizations should consider additional defensive measures:

Network Segmentation: Restrict outbound SMB connections from web servers to only necessary internal resources using firewall rules and network segmentation policies.

Service Account Hardening: Ensure Apache service accounts have minimal necessary privileges and cannot authenticate to unnecessary network resources.

SMB Signing Enforcement: Require SMB signing for all SMB communications to prevent relay attacks, though this doesn't prevent initial hash capture.

Monitoring and Detection: Implement monitoring for unusual outbound connections from web servers, particularly SMB connections to unfamiliar IP addresses or external networks.

Alternative Authentication Methods: Where possible, consider using Kerberos instead of NTLM for authentication, as it's less susceptible to relay attacks.

The Broader Context of Windows Web Server Security

CVE-2025-59775 highlights ongoing security challenges specific to Windows web server environments. Several factors contribute to the unique security landscape:

Integration with Windows Authentication: The tight integration between web applications and Windows authentication mechanisms creates potential attack surfaces that don't exist on other platforms.

Historical Protocol Vulnerabilities: NTLM has known security weaknesses that continue to be exploited in novel ways, as demonstrated by this Apache vulnerability.

Enterprise Deployment Patterns: Windows web servers in enterprise environments often have extensive network permissions and trust relationships that can be exploited through credential leaks.

This incident follows a pattern of Windows-specific vulnerabilities in cross-platform software, where features or behaviors unique to Windows create security gaps that might not be immediately apparent to developers primarily familiar with Unix-like systems.

Industry Response and Best Practices

The disclosure of CVE-2025-59775 follows responsible disclosure practices, with the Apache Software Foundation working with security researchers to develop and release patches before public disclosure. This coordinated approach helps minimize the window of opportunity for attackers while giving organizations time to prepare for updates.

Security experts recommend several best practices for organizations running web servers on Windows:

Regular Vulnerability Assessment: Conduct regular security assessments of web server configurations, particularly focusing on Windows-specific attack vectors.

Privilege Minimization: Run web servers with the least privileges necessary, avoiding domain administrator or highly privileged service accounts when possible.

Defense in Depth: Implement multiple layers of security controls rather than relying solely on patching or any single protective measure.

Timely Patching Processes: Establish efficient processes for testing and deploying security updates to web server infrastructure, with particular attention to cross-platform software running on Windows.

Looking Forward: Web Server Security Evolution

The discovery of CVE-2025-59775 underscores the continuing evolution of web server security threats, particularly those targeting the intersection of web technologies and operating system authentication systems. As organizations increasingly deploy mixed environments with both Windows and non-Windows systems, understanding platform-specific vulnerabilities becomes increasingly important.

Future security developments may include:

Enhanced Input Validation Frameworks: More robust input validation mechanisms in web server software that account for platform-specific behaviors.

Operating System Security Integration: Tighter integration between web server software and operating system security features to prevent credential leakage.

Protocol Improvements: Continued evolution away from vulnerable protocols like NTLM toward more secure authentication methods.

For now, organizations running Apache HTTP Server on Windows should prioritize upgrading to version 2.4.66 while implementing complementary security controls to protect against SSRF and credential leakage attacks. The vulnerability serves as a reminder that even mature, widely-used software can contain platform-specific security gaps that require vigilant maintenance and defense.