CVE-2021-42574 Information

Description

DISPUTED An issue was discovered in the Bidirectional Algorithm in the Unicode Specification through 14.0. It permits the visual reordering of characters via control sequences which can be used to craft source code that renders different logic than the logical ordering of tokens ingested by compilers and interpreters. Adversaries can leverage this to encode source code for compilers accepting Unicode such that targeted vulnerabilities are introduced invisibly to human reviewers. NOTE: the Unicode Consortium offers the following alternative approach to presenting this concern. An issue is noted in the nature of international text that can affect applications that implement support for The Unicode Standard and the Unicode Bidirectional Algorithm (all versions). Due to text display behavior when text includes left-to-right and right-to-left characters the visual order of tokens may be different from their logical order. Additionally control characters needed to fully support the requirements of bidirectional text can further obfuscate the logical order of tokens. Unless mitigated an adversary could craft source code such that the ordering of tokens perceived by human reviewers does not match what will be processed by a compiler/interpreter/etc. The Unicode Consortium has documented this class of vulnerability in its document Unicode Technical Report 36 Unicode Security Considerations. The Unicode Consortium also provides guidance on mitigations for this class of issues in Unicode Technical Standard 39 Unicode Security Mechanisms and in Unicode Standard Annex 31 Unicode Identifier and Pattern Syntax. Also the BIDI specification allows applications to tailor the implementation in ways that can mitigate misleading visual reordering in program text; see HL4 in Unicode Standard Annex 9 Unicode Bidirectional Algorithm.

CVSS Vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H

Reference

https://trojansource.codes http://www.unicode.org/versions/Unicode14.0.0/ http://www.openwall.com/lists/oss-security/2021/11/01/1 http://www.openwall.com/lists/oss-security/2021/11/01/4 http://www.openwall.com/lists/oss-security/2021/11/01/5 http://www.openwall.com/lists/oss-security/2021/11/01/6 http://www.openwall.com/lists/oss-security/2021/11/02/10 https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ https://www.kb.cert.org/vuls/id/999008 https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ https://www.scyon.nl/post/trojans-in-your-source-code https://www.unicode.org/reports/tr36/ https://www.unicode.org/reports/tr9/tr9-44.html#HL4 https://www.unicode.org/reports/tr31/ https://www.unicode.org/reports/tr39/

Attack Complexity

HIGH

Privileges Required

NONE

User Interaction Required

NONE

Scope

REQUIRED

Confidentiality Impact

CHANGED

Integrity Impact

HIGH

Availability Impact

HIGH

Base Score

HIGH

Base Severity

8.3