This indicates a possible attempt to exploit a buffer overflow vulnerability in the AN HTTPD web server.
The plugin cmdIS.dll is used by the server to parse a "bat" file and run it as a cgi script, calling the GetEnvironmentStrings API to get environment variables. The result from the API is not properly sanitized by the cmdSI.dll plugin before copying it into a buffer. An attacker can cause a buffer overflow by sending a GET request with oversized "user-agent", "host", or "accept-encoding" HTTP headers, resulting in a denial of service or arbitrary code execution in the web server security context.
AN HTTPd 1.42 n and earlier versions.
System compromise: remote code execution.
Apply the most recent upgrades or patches from the vendor.