CWE-77: Command Injection
Improper Neutralization of Special Elements used in a Command
The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.
How it's found
Command Injection describes a general pattern rather than a single fixed bug. Testers use a mix of static analysis and manual code review to find where a target's code matches this pattern, then confirm exploitability by hand.
Many protocols and products have their own custom command language. While OS or shell command strings are frequently discovered and targeted, developers may not realize that these other command languages might also be vulnerable to attacks.
Vulnerable vs. safe
prompt = "Explain the difference between {} and {}".format(arg1, arg2)result = invokeChatbot(prompt)resultHTML = encodeForHTML(result)print resultHTML# throw exception, generate error, etc.cweRegex = re.compile("^CWE-\d+$")match1 = cweRegex.search(arg1)match2 = cweRegex.search(arg2)if match1 is None or match2 is None:prompt = "Explain the difference between {} and {}".format(arg1, arg2)...Consequences
- Execute Unauthorized Code or Commands: If a malicious user injects a character (such as a semi-colon) that delimits the end of one command and the beginning of another, it may be possible to then insert an entirely new and unrelated command that was not intended to be executed. This gives an attacker a privilege or capability that they would not otherwise have.
Mitigations
- Architecture and Design: If at all possible, use library calls rather than external processes to recreate the desired functionality.
- Implementation: If possible, ensure that all external commands called from the program are statically created.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. 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 the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Operation: Run time: Run time policy enforcement may be used in an allowlist fashion to prevent use of any non-sanctioned commands.
- System Configuration: Assign permissions that prevent the user from accessing/opening privileged files.
How TurboPentest tests for this (white-box)
This weakness (Command Injection) is caught by white-box static analysis when you connect a GitHub repo: IntegSec's Opengrep SAST rule pack carries 9 rules for it, flagging the issue directly in your source code as part of the pentest.
Frequently asked questions
What is CWE-77?
The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.
How do you find Command Injection?
Command Injection describes a general pattern rather than a single fixed bug. Testers use a mix of static analysis and manual code review to find where a target's code matches this pattern, then confirm exploitability by hand.
What is the impact of CWE-77?
Execute Unauthorized Code or Commands: If a malicious user injects a character (such as a semi-colon) that delimits the end of one command and the beginning of another, it may be possible to then insert an entirely new and unrelated command that was not intended to be executed. This gives an attacker a privilege or capability that they would not otherwise have.
Does TurboPentest test for Command Injection?
This weakness (Command Injection) is caught by white-box static analysis when you connect a GitHub repo: IntegSec's Opengrep SAST rule pack carries 9 rules for it, flagging the issue directly in your source code as part of the pentest.
Related CWEs
Written and reviewed by
Michel Chamberland - Founder & CEO, IntegSec
CISSP, OSCP, OSCE, CEH, GIAC, CCSK · 20+ years in offensive security
Michel has spent 20+ years on offensive security teams including IBM X-Force Red and Trustwave SpiderLabs, leading penetration tests, red team engagements, and breach response for Fortune 500 customers. He is the founder of IntegSec and the architect of TurboPentest.
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