Incorrect Behavior Order: Early Validation

Opis

The product validates input before applying protection mechanisms that modify the input, which could allow an attacker to bypass the validation via dangerous inputs that only arise after the modification.

Product needs to validate data at the proper time, after data has been canonicalized and cleansed. Early validation is susceptible to various manipulations that result in dangerous inputs that are produced by canonicalization and cleansing.

Skutki

• Access Control, Integrity

  Bypass Protection Mechanism; Execute Unauthorized Code or Commands

  An attacker could include dangerous input that bypasses validation protection mechanisms which can be used to launch various attacks including injection attacks, execute arbitrary code or cause other unintended behavior.

Zapobieganie

• 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-2002-0433 List files in web server using "*.ext"
• CVE-2003-0332 Product modifies the first two letters of a filename extension after performing a security check, which allows remote attackers to bypass authentication via a filename with a .ats extension instead of a .hts extension.
• CVE-2002-0802 Database consumes an extra character when processing a character that cannot be converted, which could remove an escape character from the query and make the application subject to SQL injection attacks.
• CVE-2000-0191 Overlaps "fakechild/../realchild"
• CVE-2004-2363 Product checks URI for "<" and other literal characters, but does it before hex decoding the URI, so "%3E" and other sequences are allowed.
• CVE-2002-0934 Directory traversal vulnerability allows remote attackers to read or modify arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence.
• CVE-2003-0282 Directory traversal vulnerability allows attackers to overwrite arbitrary files via invalid characters between two . (dot) characters, which are filtered and result in a ".." sequence.

Słabość nadrzędna

• CWE-20 Improper Input Validation
• CWE-696 Incorrect Behavior Order

Słabości podrzędne

• CWE-180 Incorrect Behavior Order: Validate Before Canonicalize
• CWE-181 Incorrect Behavior Order: Validate Before Filter

Kiedy powstaje

• Implementation — Since early validation errors usually arise from improperly implemented defensive mechanisms, it is likely that these will be introduced more frequently as secure programming becomes implemented more widely.

Dotyczy

Not Language-Specific

Uwagi

These errors are mostly reported in path traversal vulnerabilities, but the concept applies whenever validation occurs.

Źródła

1. The Art of Software Security Assessment — Mark Dowd, John McDonald, Justin Schuh, Chapter 8, "Escaping Metacharacters", Page 439, Addison Wesley, 2006