CVE-2013-4547 in nginx
Summary
by MITRE
nginx 0.8.41 through 1.4.3 and 1.5.x before 1.5.7 allows remote attackers to bypass intended restrictions via an unescaped space character in a URI.
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability identified as CVE-2013-4547 affects nginx web server versions ranging from 0.8.41 through 1.4.3 and all 1.5.x versions prior to 1.5.7. This security flaw represents a critical access control bypass that enables remote attackers to circumvent intended restrictions imposed on web content through improper URI handling. The vulnerability stems from the web server's inadequate processing of unescaped space characters within Uniform Resource Identifiers, creating a pathway for unauthorized access to protected resources.
The technical implementation of this vulnerability resides in nginx's URI parsing mechanism where the server fails to properly escape or normalize space characters within URLs. When a malicious user submits a URI containing an unescaped space character, the web server processes this input in a manner that allows the request to bypass access control mechanisms. This behavior violates the expected security model where specific URI patterns should be restricted or protected, yet the unescaped space character enables the server to interpret the request differently than intended. The flaw operates at the application layer of the network stack and directly impacts the web server's ability to enforce access policies.
The operational impact of CVE-2013-4547 extends beyond simple unauthorized access to potentially enable more sophisticated attacks within the compromised environment. An attacker could exploit this vulnerability to access restricted directories, bypass authentication mechanisms, or gain access to sensitive files and resources that should be protected. The vulnerability is particularly concerning because it allows remote exploitation without requiring authentication, making it a significant threat to web server security. Organizations using affected nginx versions face the risk of data exposure, privilege escalation, and potential system compromise through this access control bypass mechanism.
This vulnerability aligns with CWE-20, "Improper Input Validation," and relates to ATT&CK technique T1190 "Exploit Public-Facing Application" through its ability to bypass web application security controls. The flaw demonstrates how seemingly minor input processing issues can result in major security consequences, particularly in web server implementations where URI handling is fundamental to access control enforcement. Organizations should implement immediate mitigation strategies including upgrading to patched nginx versions, implementing proper input validation at the web server level, and deploying additional security controls such as web application firewalls to protect against exploitation attempts. The vulnerability also highlights the importance of thorough testing of URI parsing behavior in security-critical applications and the need for comprehensive security reviews of input handling mechanisms.
The remediation approach for this vulnerability requires immediate deployment of nginx version 1.5.7 or later, which contains the necessary patches to properly handle unescaped space characters in URIs. Security administrators should conduct comprehensive testing to ensure that the upgrade does not introduce compatibility issues with existing web applications while verifying that the patched version properly enforces access control restrictions. Additionally, organizations should review their current access control policies and implement monitoring for suspicious URI patterns that might indicate exploitation attempts. This vulnerability serves as a reminder of the critical importance of proper input sanitization and URI normalization in web server implementations, particularly in environments where access control is paramount to overall security posture.