CVE-2016-3655 - Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

Severity

99%

Complexity

99%

Confidentiality

165%

The management web interface in Palo Alto Networks PAN-OS before 5.0.18, 6.0.x before 6.0.13, 6.1.x before 6.1.10, and 7.0.x before 7.0.5 allows remote attackers to execute arbitrary OS commands via an unspecified API call.

The management web interface in Palo Alto Networks PAN-OS before 5.0.18, 6.0.x before 6.0.13, 6.1.x before 6.1.10, and 7.0.x before 7.0.5 allows remote attackers to execute arbitrary OS commands via an unspecified API call.

CVSS 3.0 Base Score 9.8. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

CVSS 2.0 Base Score 9.9. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (AV:N/AC:L/Au:N/C:C/I:C/A:C).

Demo Examples

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

CWE-78

This example code intends to take the name of a user and list the contents of that user's home directory. It is subject to the first variant of OS command injection.


               
system($command);

The $userName variable is not checked for malicious input. An attacker could set the $userName variable to an arbitrary OS command such as:


               
;rm -rf /

Which would result in $command being:


               
ls -l /home/;rm -rf /

Since the semi-colon is a command separator in Unix, the OS would first execute the ls command, then the rm command, deleting the entire file system.

Also note that this example code is vulnerable to Path Traversal (CWE-22) and Untrusted Search Path (CWE-426) attacks.

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

CWE-78

This example is a web application that intends to perform a DNS lookup of a user-supplied domain name. It is subject to the first variant of OS command injection.


               
}
close($fh);
print "<br>\n";

Suppose an attacker provides a domain name like this:


               
cwe.mitre.org%20%3B%20/bin/ls%20-l

The "%3B" sequence decodes to the ";" character, and the %20 decodes to a space. The open() statement would then process a string like this:


               
/path/to/nslookup cwe.mitre.org ; /bin/ls -l

As a result, the attacker executes the "/bin/ls -l" command and gets a list of all the files in the program's working directory. The input could be replaced with much more dangerous commands, such as installing a malicious program on the server.

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

CWE-78

The example below reads the name of a shell script to execute from the system properties. It is subject to the second variant of OS command injection.


               
System.exec(script);

If an attacker has control over this property, then they could modify the property to point to a dangerous program.

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

CWE-78

In the example below, a method is used to transform geographic coordinates from latitude and longitude format to UTM format. The method gets the input coordinates from a user through a HTTP request and executes a program local to the application server that performs the transformation. The method passes the latitude and longitude coordinates as a command-line option to the external program and will perform some processing to retrieve the results of the transformation and return the resulting UTM coordinates.


               
}
return utmCoords;
// process results of coordinate transform// ...

However, the method does not verify that the contents of the coordinates input parameter includes only correctly-formatted latitude and longitude coordinates. If the input coordinates were not validated prior to the call to this method, a malicious user could execute another program local to the application server by appending '&' followed by the command for another program to the end of the coordinate string. The '&' instructs the Windows operating system to execute another program.

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

CWE-78

The following code is from an administrative web application designed to allow users to kick off a backup of an Oracle database using a batch-file wrapper around the rman utility and then run a cleanup.bat script to delete some temporary files. The script rmanDB.bat accepts a single command line parameter, which specifies what type of backup to perform. Because access to the database is restricted, the application runs the backup as a privileged user.


               
...
"&&c:\\utl\\cleanup.bat\"")

The problem here is that the program does not do any validation on the backuptype parameter read from the user. Typically the Runtime.exec() function will not execute multiple commands, but in this case the program first runs the cmd.exe shell in order to run multiple commands with a single call to Runtime.exec(). Once the shell is invoked, it will happily execute multiple commands separated by two ampersands. If an attacker passes a string of the form "& del c:\\dbms\\*.*", then the application will execute this command along with the others specified by the program. Because of the nature of the application, it runs with the privileges necessary to interact with the database, which means whatever command the attacker injects will run with those privileges as well.

Demo Examples

Improper Input Validation

CWE-20

This example demonstrates a shopping interaction in which the user is free to specify the quantity of items to be purchased and a total is calculated.


               
...

The user has no control over the price variable, however the code does not prevent a negative value from being specified for quantity. If an attacker were to provide a negative value, then the user would have their account credited instead of debited.

Improper Input Validation

CWE-20

This example asks the user for a height and width of an m X n game board with a maximum dimension of 100 squares.


               
.../* board dimensions */
die("No integer passed: Die evil hacker!\n");
die("No integer passed: Die evil hacker!\n");
die("Value too large: Die evil hacker!\n");

While this code checks to make sure the user cannot specify large, positive integers and consume too much memory, it does not check for negative values supplied by the user. As a result, an attacker can perform a resource consumption (CWE-400) attack against this program by specifying two, large negative values that will not overflow, resulting in a very large memory allocation (CWE-789) and possibly a system crash. Alternatively, an attacker can provide very large negative values which will cause an integer overflow (CWE-190) and unexpected behavior will follow depending on how the values are treated in the remainder of the program.

Improper Input Validation

CWE-20

The following example shows a PHP application in which the programmer attempts to display a user's birthday and homepage.


               
echo "Birthday: $birthday<br>Homepage: <a href=$homepage>click here</a>"

The programmer intended for $birthday to be in a date format and $homepage to be a valid URL. However, since the values are derived from an HTTP request, if an attacker can trick a victim into clicking a crafted URL with <script> tags providing the values for birthday and / or homepage, then the script will run on the client's browser when the web server echoes the content. Notice that even if the programmer were to defend the $birthday variable by restricting input to integers and dashes, it would still be possible for an attacker to provide a string of the form:


               
2009-01-09--

If this data were used in a SQL statement, it would treat the remainder of the statement as a comment. The comment could disable other security-related logic in the statement. In this case, encoding combined with input validation would be a more useful protection mechanism.

Furthermore, an XSS (CWE-79) attack or SQL injection (CWE-89) are just a few of the potential consequences when input validation is not used. Depending on the context of the code, CRLF Injection (CWE-93), Argument Injection (CWE-88), or Command Injection (CWE-77) may also be possible.

Improper Input Validation

CWE-20

This function attempts to extract a pair of numbers from a user-supplied string.


               
}
die("Did not specify integer value. Die evil hacker!\n");
/* proceed assuming n and m are initialized correctly */

This code attempts to extract two integer values out of a formatted, user-supplied input. However, if an attacker were to provide an input of the form:


               
123:

then only the m variable will be initialized. Subsequent use of n may result in the use of an uninitialized variable (CWE-457).

Improper Input Validation

CWE-20

The following example takes a user-supplied value to allocate an array of objects and then operates on the array.


               
}
list[0] = new Widget();
die("Negative value supplied for list size, die evil hacker!");

This example attempts to build a list from a user-specified value, and even checks to ensure a non-negative value is supplied. If, however, a 0 value is provided, the code will build an array of size 0 and then try to store a new Widget in the first location, causing an exception to be thrown.

Improper Input Validation

CWE-20

This application has registered to handle a URL when sent an intent:


               
}......
}
}
int length = URL.length();
...

The application assumes the URL will always be included in the intent. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called.

Overview

First reported 9 years ago

2016-04-12 17:59:00

Last updated 5 years ago

2020-02-17 16:15:00

Affected Software

Palo Alto Networks PAN-OS

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