Product Description mod_ntlm is an Apache module (originially designed for Apache 1.3, now available for Apache 2.0) that provides the ability for Apache services to authenticate users via the NTLM authentication technology that is largely specific to Microsoft IIS. Home page: http://www.sourceforge.net/projects/modntlm Vulnerability Description mod_ntlm contains a pair of remotely-exploitable vulnerabilities in its data logging routine. The vulnerabilities occur in a default build. The mod_ntlm "log()" function contains a pair of exploitable error conditions: static void log(const request_rec * r, const char *format,...) { va_list ap; char *s; if ((s = (char *) malloc(2048)) == NULL) return; va_start(ap, format); vsprintf(s, format, ap); va_end(ap); ap_log_rerror(APLOG_MARK, APLOG_NOERRNO | APLOG_NOTICE, r, s); free(s); } The function is called with user-supplied input in various locations in the code. The first vulnerability is a heap overflow -- if any user-supplied input is greater than 2048 characters, memory management structures are overwritten, and arbitrary code execution is possible. Secondly, an incorrect call to ap_log_rerror(). The last parameter to ap_log_rerror() is not a log line, but a format string. Due to the previous decoding operation, it becomes possible to pass format specifiers to ap_log_rerror(). A carefully crafted format string may allow code execution. Proof-of-Concept Either of the following two sessions will cause httpd to exit due to a segmentation fault: GET / HTTP/1.0 Authorization: [Ax3000] OR GET / HTTP/1.0 Authorization: %n%n%n%n Similarly, a proxy server can be exploited by using an external URL (http://www.yahoo.com/, for instance), in place of "/", and using Proxy-Authorization, in place of Authorization in the examples above. Vulnerable Versions Apache 1.3: mod_ntlm v0.4 and prior Apache 2.0: mod_ntlmv2 v0.1 Vendor Status The vulnerability was submitted to the vendor via SourceForge at: http://sourceforge.net/tracker/index.php?func=detail&aid=723468&group_id=490 6&atid=104906 The vendor has not responded to the bug report as of the time of writing of this advisory. _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
This archive was generated by hypermail 2b30 : Mon Apr 21 2003 - 10:53:16 PDT