CVE-2017-20005: 
NGINX vulnerability analysis and mitigation

NGINX before version 1.13.6 contains a buffer overflow vulnerability (CVE-2017-20005) that occurs when processing files with years that exceed four digits. This vulnerability is triggered when the autoindex module encounters a file with a modification date in 1969 that causes an integer overflow, or a false modification date far in the future. The vulnerability was discovered by Jamie Landeg-Jones and reported in 2017 (Nginx Ticket, Debian LTS).

The vulnerability exists in the ngxgmtime() function where various buffers are allocated with the assumption that there would be no more than 4 year digits. On platforms with 64-bit timet, this assumption doesn't hold true as 64-bit time_t can represent dates with more than 4 digits. The issue occurs when processing negative timestamps or dates far in the future, which can cause buffer overflow due to improper handling of the year field (Nginx Commit). The vulnerability has been assigned a CVSS v3.1 score of 9.8 (CRITICAL) (NetApp Advisory).

Successful exploitation of this vulnerability could lead to disclosure of sensitive information, addition or modification of data, or Denial of Service (DoS). The buffer overflow condition could potentially allow attackers to cause worker process crashes or execute arbitrary code (NetApp Advisory).

The vulnerability was fixed in NGINX version 1.13.6 by implementing time truncation to December 31, 9999, and properly handling negative timestamps. The fix ensures that all dates are truncated by ngx_gmtime() to prevent potential buffer overflows while maintaining compatibility with valid dates (Nginx Commit). Users should upgrade to NGINX version 1.13.6 or later to address this vulnerability.