Description
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as comment delimiters when they are sent to a downstream component.
Potential Impact
Integrity
Unexpected State
Mitigations & Prevention
Developers should anticipate that comments will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
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 relat
While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. 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 allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in qu
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Real-World CVE Examples
| CVE ID | Description |
|---|---|
| CVE-2002-0001 | Mail client command execution due to improperly terminated comment in address list. |
| CVE-2004-0162 | MIE. RFC822 comment fields may be processed as other fields by clients. |
| CVE-2004-1686 | Well-placed comment bypasses security warning. |
| CVE-2005-1909 | Information hiding using a manipulation involving injection of comment code into product. Note: these vulnerabilities are likely vulnerable to more general XSS problems, although a regexp might allow |
| CVE-2005-1969 | Information hiding using a manipulation involving injection of comment code into product. Note: these vulnerabilities are likely vulnerable to more general XSS problems, although a regexp might allow |
Related Weaknesses
Taxonomy Mappings
- PLOVER: — Comment Element
- Software Fault Patterns: SFP24 — Tainted input to command
Frequently Asked Questions
What is CWE-151?
CWE-151 (Improper Neutralization of Comment Delimiters) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as comment delimiters when they are sent to a do...
How can CWE-151 be exploited?
Attackers can exploit CWE-151 (Improper Neutralization of Comment Delimiters) to unexpected state. This weakness is typically introduced during the Implementation phase of software development.
How do I prevent CWE-151?
Key mitigations include: Developers should anticipate that comments will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid,
What is the severity of CWE-151?
CWE-151 is classified as a Variant-level weakness (Low-Medium abstraction). It has been observed in 5 real-world CVEs.