Double Decoding of the Same DataID: 174 | Date: (C)2012-05-14 (M)2022-10-10 |
Type: weakness | Status: DRAFT |
Abstraction Type: Variant |
Description
The software decodes the same input twice, which can limit the
effectiveness of any protection mechanism that occurs in between the decoding
operations.
Applicable PlatformsLanguage Class: All
Time Of Introduction
Common Consequences
Scope | Technical Impact | Notes |
---|
Access_ControlConfidentialityAvailabilityIntegrityOther | Bypass protection
mechanismExecute unauthorized code or
commandsVaries by context | |
Detection MethodsNone
Potential Mitigations
Phase | Strategy | Description | Effectiveness | Notes |
---|
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 whitelist 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
(i.e., do not rely on a blacklist). A blacklist 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, blacklists can be useful for detecting potential
attacks or determining which inputs are so malformed that they should be
rejected outright. | | |
Implementation | Output Encoding | 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. | | |
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 whitelist validation
schemes by introducing dangerous inputs after they have been
checked. | | |
Relationships
Related CWE | Type | View | Chain |
---|
CWE-174 ChildOf CWE-896 | Category | CWE-888 | |
Demonstrative ExamplesNone
Observed Examples
- 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-2001-0333 : Directory traversal using double encoding.
- CVE-2004-1938 : "%2527" (double-encoded single quote) used in SQL injection.
- CVE-2005-1945 : Double hex-encoded data.
- 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.
For more examples, refer to CVE relations in the bottom box.
White Box Definitions None
Black Box Definitions None
Taxynomy Mappings
Taxynomy | Id | Name | Fit |
---|
PLOVER | | Double Encoding | |
References:None