CVE-2017-20005 in Nginx
Summary
by MITRE • 06/07/2021
NGINX before 1.13.6 has a buffer overflow for years that exceed four digits, as demonstrated by a file with a modification date in 1969 that causes an integer overflow (or a false modification date far in the future), when encountered by the autoindex module.
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Analysis
by VulDB Data Team • 04/29/2026
The vulnerability CVE-2017-20005 represents a critical buffer overflow issue in NGINX web server versions prior to 1.13.6, specifically affecting the autoindex module's handling of file modification dates. This flaw demonstrates a classic integer overflow condition that occurs when processing file timestamps exceeding four digits, creating a dangerous scenario where the system's memory management becomes compromised. The vulnerability manifests when NGINX encounters files with modification dates that cannot be properly represented within the allocated buffer space, leading to potential memory corruption and system instability.
The technical implementation of this vulnerability stems from improper input validation within the autoindex module, which is responsible for generating directory listings when directory browsing is enabled. When processing file metadata, particularly modification timestamps, the system fails to adequately validate the year component of date fields, allowing for integer overflow conditions to occur. This specific flaw falls under the CWE-190 category of Integer Overflow or Wraparound, where an integer value exceeds its maximum representable value and wraps around to a much smaller value. The vulnerability is particularly concerning because it can be triggered through legitimate file system operations, making it difficult to detect and prevent through conventional security measures.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it creates potential attack vectors for more sophisticated exploitation techniques. An attacker could manipulate file timestamps to create modification dates in years that exceed four digits, causing the buffer overflow to occur during directory listing generation. This could result in memory corruption that might be leveraged for arbitrary code execution, depending on the system configuration and memory layout. The false modification dates far in the future mentioned in the vulnerability description represent a particular manifestation of this issue where the integer overflow produces unexpected and potentially exploitable values. The autoindex module's role in web server functionality makes this vulnerability particularly dangerous as it can be triggered through normal web browsing activities when directory listings are generated.
Mitigation strategies for CVE-2017-20005 primarily focus on immediate version upgrades to NGINX 1.13.6 or later, which contain the necessary patches to address the integer overflow condition in the autoindex module. Organizations should also implement strict input validation measures for file system metadata and consider disabling the autoindex module when it is not required for specific server configurations. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as exploitation could potentially involve manipulating file timestamps to trigger the vulnerable code path. Network administrators should monitor for unusual directory listing behaviors and implement proper logging to detect potential exploitation attempts. The vulnerability also highlights the importance of proper integer handling in web server components and demonstrates how seemingly benign file metadata processing can become a security risk when proper validation is not implemented. Organizations should conduct thorough vulnerability assessments to identify other potential integer overflow conditions in their web server configurations and ensure that all third-party components are regularly updated to address known security flaws.