Weakness · High
CWE-168: Improper Handling of Inconsistent Special Elements
What it is
The product does not properly handle input in which an inconsistency exists between two or more special characters or reserved words.
- Severity (our rating)
- High
- Likelihood of exploit
- Not rated by MITRE
- Introduced during
- Implementation
- Exploited in the wild
- No CVE in CISA's catalog
In more detail
An example of this problem would be if paired characters appear in the wrong order, or if the special characters are not properly nested.
What an attacker can do
- DoS: Crash, Exit, or Restart (Availability, Access Control, Non-Repudiation)
- Bypass Protection Mechanism (Availability, Access Control, Non-Repudiation)
- Hide Activities (Availability, Access Control, Non-Repudiation)
How to prevent it
General
- Developers should anticipate that inconsistent special elements will be injected/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.
Implementation
- 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.
- 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.
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Start freeSource: MITRE Common Weakness Enumeration, CWE version 4.19.1. CWE is a trademark of The MITRE Corporation.