CWE-551

Incorrect Behavior Order: Authorization Before Parsing and Canonicalization
AI Translation Available

If a web server does not fully parse requested URLs before it examines them for authorization, it may be possible for an attacker to bypass authorization protection.

Status
incomplete
Abstraction
base
Not Technology-Specific Web Based Web Server

For instance, the character strings /./ and / both mean current directory. If /SomeDirectory is a protected directory and an attacker requests /./SomeDirectory, the attacker may be able to gain access to the resource if /./ is not converted to / before the authorization check is performed.

Common Consequences

access control
Impacts
bypass protection mechanism

Potential Mitigations

Phases:
architecture and design
Descriptions:
• URL Inputs should be decoded and canonicalized to the application's current internal representation before being validated and processed for authorization. Make sure that your application does not decode the same input twice. Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked.