Ecosyste.ms: Advisories

Security Advisories: GSA_kwCzR0hTQS1ncHY1LTd4M2ctZ2hqds4AAz4I

fast-xml-parser regex vulnerability patch could be improved from a safety perspective

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.

Permalink: https://github.com/advisories/GHSA-gpv5-7x3g-ghjv
JSON: https://advisories.ecosyste.ms/api/v1/advisories/GSA_kwCzR0hTQS1ncHY1LTd4M2ctZ2hqds4AAz4I
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Low
Classification: General
Published: 11 months ago
Updated: 5 months ago

Identifiers: GHSA-gpv5-7x3g-ghjv
References:

• https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-6w63-h3fj-q4vw
• https://github.com/NaturalIntelligence/fast-xml-parser/security/advisories/GHSA-gpv5-7x3g-ghjv
• https://github.com/NaturalIntelligence/fast-xml-parser/commit/9a880b887916855c3a510869fd1ee268d7fe58b1
• https://github.com/advisories/GHSA-gpv5-7x3g-ghjv

Repository: https://github.com/NaturalIntelligence/fast-xml-parser
Blast Radius: 0.0

Affected Packages