CWE-88: Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')

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Description

The product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.

Extended Description

When creating commands using interpolation into a string, developers may assume that only the arguments/options that they specify will be processed. This assumption may be even stronger when the programmer has encoded the command in a way that prevents separate commands from being provided maliciously, e.g. in the case of shell metacharacters. When constructing the command, the developer may use whitespace or other delimiters that are required to separate arguments when the command. However, if an attacker can provide an untrusted input that contains argument-separating delimiters, then the resulting command will have more arguments than intended by the developer. The attacker may then be able to change the behavior of the command. Depending on the functionality supported by the extraneous arguments, this may have security-relevant consequences.

ThreatScore

Threat Mapped score: 0.0

Industry: Finiancial

Threat priority: Unclassified

Observed Examples (CVEs)

Related Attack Patterns (CAPEC)

Attack TTPs

N/A

Modes of Introduction

Phase Note
Implementation REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Common Consequences

Potential Mitigations

Applicable Platforms

Demonstrative Examples

Intro: Consider the following program. It intends to perform an "ls -l" on an input filename. The validate_name() subroutine performs validation on the input to make sure that only alphanumeric and "-" characters are allowed, which avoids path traversal (CWE-22) and OS command injection (CWE-78) weaknesses. Only filenames like "abc" or "d-e-f" are intended to be allowed.

Body: However, validate_name() allows filenames that begin with a "-". An adversary could supply a filename like "-aR", producing the "ls -l -aR" command (CWE-88), thereby getting a full recursive listing of the entire directory and all of its sub-directories. There are a couple possible mitigations for this weakness. One would be to refactor the code to avoid using system() altogether, instead relying on internal functions. Another option could be to add a "--" argument to the ls command, such as "ls -l --", so that any remaining arguments are treated as filenames, causing any leading "-" to be treated as part of a filename instead of another option. Another fix might be to change the regular expression used in validate_name to force the first character of the filename to be a letter or number, such as:

my $arg = GetArgument("filename"); do_listing($arg); sub do_listing { my($fname) = @_; if (! validate_name($fname)) { print "Error: name is not well-formed!\n"; return; } # build command my $cmd = "/bin/ls -l $fname"; system($cmd); } sub validate_name { my($name) = @_; if ($name =~ /^[\w\-]+$/) { return(1); } else { return(0); } }

Intro: CVE-2016-10033 / [REF-1249] provides a useful real-world example of this weakness within PHPMailer.

Body: The program calls PHP's mail() function to compose and send mail. The fifth argument to mail() is a set of parameters. The program intends to provide a "-fSENDER" parameter, where SENDER is expected to be a well-formed email address. The program has already validated the e-mail address before invoking mail(), but there is a lot of flexibility in what constitutes a well-formed email address, including whitespace. With some additional allowed characters to perform some escaping, the adversary can specify an additional "-o" argument (listing an output file) and a "-X" argument (giving a program to execute). Additional details for this kind of exploit are in [REF-1250].

Notes

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