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GHSA-gpv5-7x3g-ghjv
No affected components available
Summary
This is a comment on https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-6w63-h3fj-q4vw and the patches fixing it.
Details
The code which validates a name calls the validator: https://github.com/NaturalIntelligence/fast-xml-parser/blob/ecf6016f9b48aec1a921e673158be0773d07283e/src/xmlparser/DocTypeReader.js#L145-L153 This checks for the presence of an invalid character. Such an approach is always risky, as it is so easy to forget to include an invalid character in the list. A safer approach is to validate entity names against the XML specification: https://www.w3.org/TR/xml11/#sec-common-syn - an ENTITY name is a Name:
[4] NameStartChar ::= ":" | [A-Z] | "_" | [a-z] | [#xC0-#xD6] | [#xD8-#xF6] | [#xF8-#x2FF] | [#x370-#x37D] |
[#x37F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] |
[#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF]
[4a] NameChar ::= NameStartChar | "-" | "." | [0-9] | #xB7 | [#x0300-#x036F] | [#x203F-#x2040]
[5] Name ::= NameStartChar (NameChar)*
so the safest way to validate an entity name is to build a regex to represent this expression and check whether the name given matches the regex. (Something along the lines of /^[name start char class][name char class]*$/.) There's probably a nice way to simplify the explicit list rather than typing it out verbatim using Unicode character properties, but I don't know enough to do so.
Measures severity based on intrinsic characteristics of the vulnerability, independent of environment.
No exploitation activity has been observed at this time. Continue routine monitoring.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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