406
Alternate Terms
White space :
Common Consequences
Scope Impact Likelihood
Integrity Unexpected State
Potential Mitigations
Developers should anticipate that whitespace 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-2002-0637 MIE. virus protection bypass with RFC violations involving extra whitespace, or
missing whitespace.
https://www.cve.org/CVERecord?id=CVE-2002-0637
CVE-2004-0942 CPU consumption with MIME headers containing lines with many space
characters, probably due to algorithmic complexity (RESOURCE.AMP.ALG).
https://www.cve.org/CVERecord?id=CVE-2004-0942
CVE-2003-1015 MIE. whitespace interpreted differently by mail clients.
https://www.cve.org/CVERecord?id=CVE-2003-1015
CWE Version 4.14
CWE-157: Failure to Sanitize Paired Delimiters
CWE-157: Failure to Sanitize Paired Delimiters