Encoding Error
Draft Class
Structure: Simple
Description
The product does not properly encode or decode the data, resulting in unexpected values.
Common Consequences 1
Scope: Integrity
Impact: Unexpected State
Potential Mitigations 3
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 (Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')).
Phase: Implementation
Strategy: Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (Incorrect Behavior Order: Validate Before Canonicalize). Make sure that the application does not decode the same input twice (Double Decoding of the Same Data). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
Observed Examples 4
CVE-2004-1315Forum software improperly URL decodes the highlight parameter when extracting text to highlight, which allows remote attackers to execute arbitrary PHP code by double-encoding the highlight value so that special characters are inserted into the result.
CVE-2004-1939XSS protection mechanism attempts to remove "/" that could be used to close tags, but it can be bypassed using double encoded slashes (%252F)
CVE-2001-0709Server allows a remote attacker to obtain source code of ASP files via a URL encoded with Unicode.
CVE-2005-2256Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"
Applicable Platforms
Languages:
Not Language-Specific : Undetermined
Modes of Introduction
Implementation
Related Attack Patterns
- 3DEPRECATED: Technology-specific Environment Issues
- 52Path Equivalence: '/multiple/trailing/slash//'
- 53Path Equivalence: '\multiple\\internal\backslash'
- 64Windows Shortcut Following (.LNK)
- 71DEPRECATED: Apple '.DS_Store'
- 72Improper Handling of Apple HFS+ Alternate Data Stream Path
- 78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
- 80Improper Neutralization of Script-Related HTML Tags in a Web Page (Basic XSS)
- 120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
- 267Privilege Defined With Unsafe Actions
Related Weaknesses
Taxonomy Mapping
- PLOVER
Notes
RelationshipPartially overlaps path traversal and equivalence weaknesses.
MaintenanceThis is more like a category than a weakness.
MaintenanceMany other types of encodings should be listed in this category.