Weakness · High

CWE-77: Improper Neutralization of Special Elements used in a Command ('Command Injection')

What it is

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.

Likelihood of exploit: High31 exploited in the wildMITRE CWE 4.19.1

Severity (our rating): High
Likelihood of exploit: High
Introduced during: Implementation
Exploited in the wild: 31 known exploited CVEs

In more detail

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.

What an attacker can do

Execute Unauthorized Code or Commands (Integrity, Confidentiality, Availability)

How to prevent it

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.
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 to find it

Automated Static Analysis. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

CWE-77 on MITRE's CWE site

Exploited in the wild: 31 CVEs

Vulnerabilities caused by CWE-77 that attackers have used, from CISA's Known Exploited Vulnerabilities catalog, newest first.

All known exploited vulnerabilities

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Source: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.