The system or application is vulnerable to file system contents
disclosure through path equivalence. Path equivalence involves the use of
special characters in file and directory names. The associated manipulations are
intended to generate multiple names for the same object.
Extended Description
Path equivalence is usually employed in order to circumvent access
controls expressed using an incomplete set of file name or file path
representations. This is different from path traversal, wherein the
manipulations are performed to generate a name for a different
object.
Time of Introduction
Implementation
Applicable Platforms
Languages
All
Potential Mitigations
Phase
Description
Architecture and Design
Assume all input is malicious. Use a standard input validation
mechanism to validate all input for length, type, syntax, and business
rules before accepting the data to be displayed or stored. Use an
"accept known good" validation strategy. Input (specifically, unexpected
CRLFs) that is not appropriate should not be processed into HTTP
headers.
Use and specify a strong output encoding (such as ISO 8859-1 or UTF
8).
Do not rely exclusively on blacklist validation to detect malicious
input or to encode output. There are too many variants to encode a
character; you're likely to miss some variants.
Inputs should be decoded and canonicalized to the application's
current internal representation before being validated. Make sure that
your application does not decode the same input twice. Such errors could
be used to bypass whitelist schemes by introducing dangerous inputs
after they have been checked.
Other Notes
Some of these manipulations could be effective in path traversal issues,
too.
Description
