CVE-2021-42574

 

Published at: - 01-11-2021 05:15

Last modified: - 25-10-2022 06:38

Total changes: - 8

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.

Common Vulnerability Scoring System (CVSS)

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

 

Verification logic

 

Reference

• https://trojansource.codes
• http://www.unicode.org/versions/Unicode14.0.0/
• [oss-security] 20211101 CVE-2021-42574: rustc 1.56.0 and bidirectional-override codepoints in source code-Exploit, Mailing List, Mitigation, Third Party Advisory
• [oss-security] 20211101 Re: CVE-2021-42574: rustc 1.56.0 and bidirectional-override codepoints in source code-Exploit, Mailing List, Third Party Advisory
• [oss-security] 20211102 Re: CVE-2021-42574: rustc 1.56.0 and bidirectional-override codepoints in source code-Mailing List, Third Party Advisory
• [oss-security] 20211101 Trojan Source Attacks-Mailing List, Third Party Advisory
• [oss-security] 20211102 Re: Trojan Source Attacks-Mailing List
• FEDORA-2021-0578e23912-Mailing List, Third Party Advisory
• FEDORA-2021-7ad3a01f6a-Mailing List, Third Party Advisory
• VU#999008-Third Party Advisory, US Government Resource
• FEDORA-2021-443139f67c-Mailing List, Third Party Advisory
• 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/
• https://www.starwindsoftware.com/security/sw-20220804-0002/
• GLSA-202210-09-Third Party Advisory

 

Keywords

NVD

 

CVE-2021-42574

 

CVE

 

Common vulnerabilities & exposures

 

CVSS

 

Common vulnerability scoring system

 

Security

 

Vulnerabilities

 

Exposures