CVE-2026-27654 in NGINX Open Source
Summary
by MITRE • 03/24/2026
NGINX Open Source and NGINX Plus have a vulnerability in the ngx_http_dav_module module that might allow an attacker to trigger a buffer overflow to the NGINX worker process; this vulnerability may result in termination of the NGINX worker process or modification of source or destination file names outside the document root. This issue affects NGINX Open Source and NGINX Plus when the configuration file uses DAV module MOVE or COPY methods, prefix location (nonregular expression location configuration), and alias directives. The integrity impact is constrained because the NGINX worker process user has low privileges and does not have access to the entire system. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability identified as CVE-2026-27654 resides within the ngx_http_dav_module component of NGINX Open Source and NGINX Plus software versions, representing a critical buffer overflow condition that could be exploited by remote attackers to compromise the stability and integrity of affected systems. This flaw specifically manifests when the DAV module's MOVE or COPY methods are utilized in conjunction with prefix location configurations and alias directives within the NGINX configuration files. The buffer overflow occurs during the processing of file operations that involve these specific module configurations, creating a potential attack vector that could be leveraged to disrupt service availability or manipulate file system access patterns beyond intended boundaries.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the DAV module's handling of file path operations. When NGINX processes MOVE or COPY requests through the affected module, the system fails to properly validate the length and content of file paths being processed, allowing maliciously crafted input to overflow allocated buffer space within the worker process memory. This buffer overflow condition creates opportunities for arbitrary code execution or process termination, as the overflow can overwrite critical memory segments including return addresses and program state variables. The vulnerability is particularly concerning because it can be triggered through standard HTTP DAV operations that are commonly enabled in web server configurations, making it accessible to attackers who can submit crafted HTTP requests to the affected service.
From an operational impact perspective, this vulnerability presents a significant risk to NGINX server availability and data integrity. The most direct consequence is the potential for NGINX worker process termination, which would result in service disruption for all users of that particular worker process. However, the more insidious aspect involves the possibility of path manipulation that allows attackers to modify file names outside the designated document root directory. This capability could enable unauthorized access to sensitive files or the ability to overwrite critical system files, depending on the privileges of the NGINX worker process. The low privilege constraint mentioned in the vulnerability description indicates that while the attack surface is limited, the potential for escalation remains a concern, particularly in environments where the NGINX process has elevated permissions or where the server configuration allows for broader file system access.
The security implications of this vulnerability extend beyond simple service disruption, as it can be classified under CWE-121, which describes heap-based buffer overflow conditions, and aligns with ATT&CK technique T1059 for execution through command and scripting interpreters. The affected configurations involving prefix location and alias directives create additional attack vectors by providing attackers with multiple pathways to manipulate the vulnerable code path. Organizations implementing NGINX with DAV functionality should consider this vulnerability in their risk assessment frameworks, particularly when evaluating their web application security posture and incident response capabilities. The End of Technical Support status of older versions means that affected systems may not receive security patches, further emphasizing the importance of immediate remediation efforts.
Mitigation strategies should prioritize the immediate disabling of DAV functionality when not required, or the implementation of proper input validation and sanitization measures within the NGINX configuration. Organizations should also consider implementing network-level controls such as web application firewalls to monitor and filter potentially malicious DAV operations, while ensuring that NGINX worker processes run with minimal necessary privileges. The most effective long-term solution involves upgrading to patched versions of NGINX software, though this requires careful planning to avoid service disruption. Additionally, implementing comprehensive monitoring for unusual file operations and system behavior can help detect exploitation attempts, while regular security assessments should verify that no other vulnerable configurations exist within the organization's web infrastructure.