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Description
The software decodes the same input twice, which can limit the effectiveness of any protection mechanism that occurs in between the decoding operations.
Modes of Introduction:
– Implementation
Related Weaknesses
CWE-172
CWE-675
Consequences
Access Control, Confidentiality, Availability, Integrity, Other: Bypass Protection Mechanism, Execute Unauthorized Code or Commands, Varies by Context
Potential Mitigations
Phase: Architecture and Design
Description:
Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
Phase: Implementation
Description:
Phase: Implementation
Description:
Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.
Phase: Implementation
Description:
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.
CVE References
- 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 that special characters are inserted into the result.
- 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-2004-1938
- “%2527” (double-encoded single quote) used in SQL injection.
- CVE-2005-0054
- Browser executes HTML at higher privileges via URL with hostnames that are double hex encoded, which are decoded twice to generate a malicious hostname.
