History[ edit ] Eric Berne presented transactional analysis to the world as a phenomenological approach supplementing Freud's philosophical construct with observable data.
High Discussion Your software is often the bridge between an outsider on the network and the internals of your operating system. When you invoke another program An analysis of most dangerous game the operating system, but you allow untrusted inputs to be fed into the command string that you generate for executing that program, then you are inviting attackers to cross that bridge into a land of riches by executing their own commands instead of yours.
Prevention and Mitigations Architecture and Design If at all possible, use library calls rather than external processes to recreate the desired functionality. Architecture and Design, Operation Run your code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system.
This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by your software. In general, managed code may provide some protection. FilePermission in the Java SecurityManager allows you to specify restrictions on file operations.
This may not be a feasible solution, and it only limits the impact to the operating system; the rest of your application may still be subject to compromise. Be careful to avoid CWE and other weaknesses related to jails. The effectiveness of this mitigation depends on the prevention capabilities of the specific sandbox or jail being used and might only help to reduce the scope of an attack, such as restricting the attacker to certain system calls or limiting the portion of the file system that can be accessed.
Architecture and Design For any data that will be used to generate a command to be executed, keep as much of that data out of external control as possible.
For example, in web applications, this may require storing the data locally in the session's state instead of sending it out to the client in a hidden form field. Architecture and Design For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely.
Then, these modified values would be submitted to the server. Architecture and Design Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
These will help the programmer encode outputs in a manner less prone to error. Implementation If you need to use dynamically-generated query strings or commands in spite of the risk, properly quote arguments and escape any special characters within those arguments.
The most conservative approach is to escape or filter all characters that do not pass an extremely strict whitelist such as everything that is not alphanumeric or white space. Be careful of argument injection CWE Implementation If the program to be executed allows arguments to be specified within an input file or from standard input, then consider using that mode to pass arguments instead of the command line.
Architecture and Design If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.
Some languages offer multiple functions that can be used to invoke commands. Where possible, identify any function that invokes a command shell using a single string, and replace it with a function that requires individual arguments. These functions typically perform appropriate quoting and filtering of arguments.
For example, in C, the system function accepts a string that contains the entire command to be executed, whereas execlexecveand others require an array of strings, one for each argument.
In Windows, CreateProcess only accepts one command at a time. In Perl, if system is provided with an array of arguments, then it will quote each of the arguments.
Implementation Assume all input is malicious.
Use an "accept known good" input validation strategy, i. Reject any input that does not strictly conform to specifications, or transform it into something that does. Do not rely exclusively on looking for malicious or malformed inputs i.
However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules.
As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if you are expecting colors such as "red" or "blue.
This will indirectly limit the scope of an attack, but this technique is less important than proper output encoding and escaping. Note that proper output encoding, escaping, and quoting is the most effective solution for preventing OS command injection, although input validation may provide some defense-in-depth.
This is because it effectively limits what will appear in output. Input validation will not always prevent OS command injection, especially if you are required to support free-form text fields that could contain arbitrary characters.
In this case, stripping the character might reduce the risk of OS command injection, but it would produce incorrect behavior because the subject field would not be recorded as the user intended. This might seem to be a minor inconvenience, but it could be more important when the program relies on well-structured subject lines in order to pass messages to other components.
Even if you make a mistake in your validation such as forgetting one out of input fieldsappropriate encoding is still likely to protect you from injection-based attacks.A mere 25 miles off the shore of Palawan sits the frontier of an increasingly dangerous and unpredictable struggle.
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