#JAVA HIGH CODEPOINTS CODE#
Where the output character set is not Unicode, though, this character may not be available.” Risk Assessmentĭeleting noncharacter code points can allow malicious input to bypass validation checks.ĬWE-182. That is, because it doesn’t have syntactic meaning in programming languages or structured data, it will typically just cause a failure in parsing. ("Found blacklisted tag") Īccording to the Unicode Technical Report #36, Unicode Security Considerations, “ U+FFFD is usually unproblematic, because it is designed expressly for this kind of purpose. Replaces all non-valid characters with unicode U+FFFD This ensures that malicious input cannot bypass filters. It also does this replacement before doing any other sanitization, in particular, checking for.
This compliant solution replaces the unknown or unrepresentable character with Unicode sequence \uFFFD, which is reserved to denote this condition. "\uFEFF" is a non-character code point Consequently, an attacker can disguise a tag and bypass the validation checks. Input validation is being performed before the deletion of non-ASCII characters. It also checks for the existence of a tag. This noncompliant code example accepts only valid ASCII characters and deletes any non-ASCII characters. In that case, the sensitive sequence of characters is formed, and can lead to a security breach.Īny string modifications, including the removal or replacement of noncharacter code points, must be performed before any validation of the string is performed. However, suppose that later on, past the gateway, an internal process invisibly deletes the X. The issue is the following: A gateway might be checking for a sensitive sequence of characters, say “delete.” If what is passed in is “deXlete,” where X is a noncharacter, the gateway lets it through: The sequence “deXlete” may be in and of itself harmless.
Whenever a character is invisibly deleted (instead of replaced), such as in this older version of C7, it may cause a security problem. When a process purports not to modify the interpretation of a valid coded character sequence, it shall make no change to that coded character sequence other than the possible replacement of character sequences by their canonical-equivalent sequences or the deletion of noncharacter code points.Īccording to the Unicode Technical Report #36, Unicode Security Considerations, Section 3.5, “Deletion of Noncharacters”: For example, conformance clause C7 from Unicode 5.1 states : In some versions prior to Unicode 5.2, conformance clause C7 allows the deletion of noncharacter code points. Eliminate noncharacter code points before validation CERT Oracle Secure Coding Standard for Java, The
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