Typical severity: High. Likelihood of attack: High. This attack targets the use of the backslash in alternate encoding. An adversary can provide a backslash as a leading character and causes a parser to believe that the next character is special. This is called an escape. By using that trick, the adversary tries to exploit alternate ways to encode the same character which leads to filter problems and opens avenues to attack.
Verify that the user-supplied data does not use backslash character to escape malicious characters. | Assume all input is malicious. Create an allowlist that defines all valid input to the software system based on the requirements specifications. Input that does not match against the allowlist should not be permitted to enter into the system. | Be aware of the threat of alternative method of data encoding. | Regular expressions can be used to filter out backslash. Make sure you decode before filtering and validating the untrusted input data. | In the case of path traversals, use the principle of least privilege when determining access rights to file systems. Do not allow users to access directories/files that they should not access.