Improper Handling of URL Encoding (Hex Encoding)

Opis

The product does not properly handle when all or part of an input has been URL encoded.

Skutki

• Integrity

  Unexpected State

Zapobieganie

• Architecture and Design · Input Validation

  Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.

• Implementation · 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.

• Implementation · 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.

Przykłady podatności

• CVE-2000-0900 Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"
• CVE-2005-2256 Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"
• CVE-2004-2121 Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"
• CVE-2004-0280 "%20" (encoded space)
• CVE-2003-0424 "%20" (encoded space)
• CVE-2001-0693 "%20" (encoded space)
• CVE-2001-0778 "%20" (encoded space)
• CVE-2002-1831 Crash via hex-encoded space "%20".
• CVE-2000-0671 "%00" (encoded null)
• CVE-2004-0189 "%00" (encoded null)
• CVE-2002-1291 "%00" (encoded null)
• CVE-2002-1031 "%00" (encoded null)
• CVE-2001-1140 "%00" (encoded null)
• CVE-2004-0760 "%00" (encoded null)
• CVE-2002-1025 "%00" (encoded null)
• CVE-2002-1213 "%2f" (encoded slash)
• CVE-2004-0072 "%5c" (encoded backslash) and "%2e" (encoded dot) sequences
• CVE-2004-0847 web framework for .NET allows remote attackers to bypass authentication for .aspx files in restricted directories via a request containing a (1) "\" (backslash) or (2) "%5C" (encoded backslash)
• CVE-2002-1575 "%0a" (overlaps CRLF)

Słabość nadrzędna

• CWE-172 Encoding Error

Kiedy powstaje

• Implementation

Dotyczy

Not Language-Specific