436
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
Use and specify an output encoding that can be handled by the downstream component that
is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an
encoding is not specified, a downstream component may choose a different encoding, either
by assuming a default encoding or automatically inferring which encoding is being used, which
can be erroneous. When the encodings are inconsistent, the downstream component might
treat some character or byte sequences as special, even if they are not special in the original
encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks;
they even might be able to bypass protection mechanisms that assume the original encoding is
also being used by the downstream component.
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.
MemberOf Relationships
This MemberOf relationships table shows additional CWE Catgeories and Views that reference this
weakness as a member. This information is often useful in understanding where a weakness fits
within the context of external information sources.
Nature Type ID Name Page
MemberOf 884 CWE Cross-section 884 2567
MemberOf 992 SFP Secondary Cluster: Faulty Input Transformation 888 2416
MemberOf 1407 Comprehensive Categorization: Improper Neutralization 1400 2532
Taxonomy Mappings
Mapped Taxonomy Name Node ID Fit Mapped Node Name
PLOVER Alternate Encoding
Related Attack Patterns
CAPEC-ID Attack Pattern Name
3 Using Leading 'Ghost' Character Sequences to Bypass Input Filters
4 Using Alternative IP Address Encodings
52 Embedding NULL Bytes
53 Postfix, Null Terminate, and Backslash
64 Using Slashes and URL Encoding Combined to Bypass Validation Logic
71 Using Unicode Encoding to Bypass Validation Logic
72 URL Encoding
78 Using Escaped Slashes in Alternate Encoding
79 Using Slashes in Alternate Encoding
80 Using UTF-8 Encoding to Bypass Validation Logic
120 Double Encoding
CWE Version 4.14
CWE-174: Double Decoding of the Same Data
CWE-174: Double Decoding of the Same Data