CVE-1999-0776 in Alibaba
Summary
by MITRE
Alibaba HTTP server allows remote attackers to read files via a .. (dot dot) attack.
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Analysis
by VulDB Data Team • 10/22/2025
The vulnerability identified as CVE-1999-0776 represents a critical directory traversal flaw in the Alibaba HTTP server implementation that enables remote attackers to access files outside the intended web root directory. This issue stems from inadequate input validation and path handling mechanisms within the server software, allowing malicious users to manipulate file access requests through directory traversal sequences. The vulnerability specifically exploits the absence of proper sanitization for directory path components, particularly the ".." (dot dot) sequence that is commonly used to navigate up directory levels in file systems.
This directory traversal vulnerability operates at the core of web server security architecture by exploiting the fundamental assumption that user-supplied input should be properly validated before being processed in file system operations. When an attacker constructs a malicious URL containing directory traversal sequences, the server fails to adequately sanitize these inputs, resulting in the unintended exposure of files that should remain protected within restricted directories. The flaw essentially allows attackers to bypass normal access controls and retrieve sensitive information from the file system, including configuration files, source code, database files, and other confidential data that may be stored on the server.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass potential system compromise and data breach scenarios. Attackers can leverage this weakness to access critical system files, application source code, database credentials, and other sensitive materials that could facilitate further exploitation. The vulnerability affects the server's ability to maintain proper isolation between different application components and user-accessible resources, potentially enabling attackers to escalate their privileges or gain unauthorized access to backend systems. This type of flaw directly violates the principle of least privilege and can lead to complete system compromise if sensitive files containing authentication credentials or system configurations are accessible through the traversal attack.
The technical nature of this vulnerability aligns with CWE-22, which categorizes directory traversal attacks as a common weakness in web applications and server implementations. This classification reflects the fundamental security principle that input validation must occur at multiple levels within application architectures, particularly when processing user-supplied data that may influence file system operations. The attack vector typically involves constructing URLs with sequences like "../../../etc/passwd" or similar patterns that allow navigation beyond the intended document root. From an adversarial perspective, this vulnerability maps to several ATT&CK techniques including T1083 (File and Directory Discovery) and T1566 (Phishing with Social Engineering) as attackers can use this weakness to discover and exfiltrate sensitive files that may contain credentials or system information.
Mitigation strategies for CVE-1999-0776 require comprehensive input validation and proper path sanitization mechanisms within the web server implementation. Organizations should implement strict validation of all user-supplied input that influences file system operations, ensuring that directory traversal sequences are properly detected and rejected. The recommended approach involves implementing robust path normalization and canonicalization processes that strip or reject any components containing ".." sequences or other potentially dangerous path elements. Additionally, server configurations should enforce proper access controls and privilege separation, limiting the web server's ability to access system files outside the designated document root. Security updates and patches should be applied immediately to address this vulnerability, while network segmentation and intrusion detection systems can help monitor for suspicious directory traversal attempts. Regular security assessments and code reviews should focus on identifying similar path traversal vulnerabilities in web applications and server configurations to prevent similar issues from occurring in other components of the information system infrastructure.