In this situation, you need to terminate the quoted context (using " or ') before using suitable shell metacharacters to inject a new command. Sometimes, the input that you control appears within quotation marks in the original command.
Note that the different shell metacharacters have subtly different behaviors that might affect whether they work in certain situations, and whether they allow in-band retrieval of command output or are useful only for blind exploitation. On Unix-based systems, you can also use backticks or the dollar character to perform inline execution of an injected command within the original command: The following command separators work only on Unix-based systems:
What is a cpp command post platform windows#
The following command separators work on both Windows and Unix-based systems: LAB Blind OS command injection with out-of-band data exfiltration Ways of injecting OS commandsĪ variety of shell metacharacters can be used to perform OS command injection attacks.Ī number of characters function as command separators, allowing commands to be chained together. This command will cause the application to ping its loopback network adapter for 10 seconds. The ping command is an effective way to do this, as it lets you specify the number of ICMP packets to send, and therefore the time taken for the command to run: You can use an injected command that will trigger a time delay, allowing you to confirm that the command was executed based on the time that the application takes to respond. In this situation, you can use a variety of other techniques to detect and exploit a vulnerability.ĭetecting blind OS command injection using time delays Mail -s "This site is great" output from the mail command (if any) is not returned in the application's responses, and so using the echo payload would not be effective. To do this, it calls out to the mail program with the submitted details. The server-side application then generates an email to a site administrator containing the feedback. The user enters their email address and feedback message. Blind vulnerabilities can still be exploited, but different techniques are required.Ĭonsider a web site that lets users submit feedback about the site. This means that the application does not return the output from the command within its HTTP response. Many instances of OS command injection are blind vulnerabilities. Below is a summary of some commands that are useful on Linux and Windows platforms:īlind OS command injection vulnerabilities When you have identified an OS command injection vulnerability, it is generally useful to execute some initial commands to obtain information about the system that you have compromised. LAB OS command injection, simple case Useful commands This reduces the likelihood that what follows will prevent the injected command from executing. Placing the additional command separator & after the injected command is generally useful because it separates the injected command from whatever follows the injection point. The original argument 29 was executed as a command, which caused an error. The injected echo command was executed, and the supplied string was echoed in the output.
The original command was executed without its expected arguments, and so returned an error message. The three lines of output demonstrate that: As a result, the output returned to the user is: The & character is a shell command separator, and so what gets executed is actually three separate commands one after another.
The echo command simply causes the supplied string to be echoed in the output, and is a useful way to test for some types of OS command injection. If this input is submitted in the productID parameter, then the command executed by the application is: Since the application implements no defenses against OS command injection, an attacker can submit the following input to execute an arbitrary command: This command outputs the stock status for the specified item, which is returned to the user. For historical reasons, the functionality is implemented by calling out to a shell command with the product and store IDs as arguments: To provide the stock information, the application must query various legacy systems. This information is accessed via a URL like: Consider a shopping application that lets the user view whether an item is in stock in a particular store.
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