Description
The product does not properly encode or decode the data, resulting in unexpected values.
Potential Impact
Integrity
Unexpected State
Mitigations & Prevention
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-2004-1315 | Forum 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 t |
| CVE-2004-1939 | XSS protection mechanism attempts to remove "/" that could be used to close tags, but it can be bypassed using double encoded slashes (%252F) |
| CVE-2001-0709 | Server allows a remote attacker to obtain source code of ASP files via a URL encoded with Unicode. |
| CVE-2005-2256 | Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e" |
Related Weaknesses
Taxonomy Mappings
- PLOVER: — Encoding Error
Frequently Asked Questions
What is CWE-172?
CWE-172 (Encoding Error) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Class-level weakness. The product does not properly encode or decode the data, resulting in unexpected values.
How can CWE-172 be exploited?
Attackers can exploit CWE-172 (Encoding Error) to unexpected state. This weakness is typically introduced during the Implementation phase of software development.
How do I prevent CWE-172?
Key mitigations include: 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 stric
What is the severity of CWE-172?
CWE-172 is classified as a Class-level weakness (High abstraction). It has been observed in 4 real-world CVEs.