397
Common Consequences
Scope Impact Likelihood
Integrity Unexpected State
Potential Mitigations
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.
Phase: Implementation
Strategy = Input Validation
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.
Phase: Implementation
Strategy = Output Encoding
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 quotes after the escaping/filtering step. Be careful of argument injection
(CWE-88).
Phase: Implementation
Strategy = Input Validation
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.
Observed Examples
Reference Description
CVE-2002-0001 Mail client command execution due to improperly terminated comment in
address list.
https://www.cve.org/CVERecord?id=CVE-2002-0001
CVE-2004-0162 MIE. RFC822 comment fields may be processed as other fields by clients.
https://www.cve.org/CVERecord?id=CVE-2004-0162
CVE-2004-1686 Well-placed comment bypasses security warning.
https://www.cve.org/CVERecord?id=CVE-2004-1686
CVE-2005-1909 Information hiding using a manipulation involving injection of comment code
into product. Note: these vulnerabilities are likely vulnerable to more general
CWE Version 4.14
CWE-152: Improper Neutralization of Macro Symbols
CWE-152: Improper Neutralization of Macro Symbols