I have a CGI script (compiled C program) that outputs its command line arguments (argv[0], argv[1] etc.).
If I try http://ajf.me/c/?abc I get “abc” as the second parameter.
However, if I try http://ajf.me/c/?a=bc I do not get any second parameter.
Why does using = stop the parameters from being passed to the program?
If it matters here is the C code:
#include <stdio.h>
int main (int argc, char *argv[]) {
int i;
printf("Content-Type: text/html;charset=utf-8\n\n");
printf("<!DOCTYPE html>\n");
printf("<html>\n");
printf("<head>\n");
printf("<title>ajf.me powered by ANSI C!</title>\n");
printf("</head>\n");
printf("<body>\n");
printf("<h2>Supplied Arguments</h2>\n");
printf("argc: %d\n", argc);
printf("<ol>\n");
for (i = 0; i < argc; ++i) {
printf("<li>%s</li>\n", argv[i]);
}
printf("</ol>\n");
printf("<em>Yes, this is vulnerable to null-byte injection. For instance, <a href=\"?Injected%%00Null\" style=\"font-family: monospace; color: green;\">?Injected\\0Null</a>.</em>\n");
printf("</body>\n");
printf("</html>\n");
}
Passing parameters to a CGI program on its command line must be an anomaly of your web server. Normally the part after the
?is available in an environment variable calledQUERY_STRING.It would probably be worthwhile for you to review the CGI specification.