Vulnerability Report

CVE-2021-42574

Title: Unicode Bidirectional Algorithm Visual Reordering Vulnerability (Trojan Source)

Code Injection

Proof Of Concept

PoC Available for CVE-2021-42574

CWE Category CWE-94
Published Date Nov 01, 2021
Modified Date Nov 21, 2024
Exploit Status Available
Score 8.3 CVSS v3.1
Exploit Probability (EPSS)
24.99%

Vulnerability Summary

CVE-2021-42574: 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.

Impacted Vendors

S
starwindsoftware 1
U
unicode_project 1
U
unicode 1

Reference Links

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 http://www.unicode.org/versions/Unicode14.0.0/ https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ https://security.gentoo.org/glsa/202210-09 https://trojansource.codes https://www.kb.cert.org/vuls/id/999008 https://www.scyon.nl/post/trojans-in-your-source-code https://www.starwindsoftware.com/security/sw-20220804-0002/ https://www.unicode.org/reports/tr31/ https://www.unicode.org/reports/tr36/ https://www.unicode.org/reports/tr39/ https://www.unicode.org/reports/tr9/tr9-44.html#HL4 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 http://www.unicode.org/versions/Unicode14.0.0/ https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ https://security.gentoo.org/glsa/202210-09 https://trojansource.codes https://www.kb.cert.org/vuls/id/999008 https://www.scyon.nl/post/trojans-in-your-source-code https://www.starwindsoftware.com/security/sw-20220804-0002/ https://www.unicode.org/reports/tr31/ https://www.unicode.org/reports/tr36/ https://www.unicode.org/reports/tr39/ https://www.unicode.org/reports/tr9/tr9-44.html#HL4
CVSS v3.1
Source Entity [email protected]
Severity HIGH
8.3
Attack Vector
NETWORK
Complexity
HIGH
Privileges
N/A
Interaction
REQUIRED
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
CHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H
CVSS v2.0
Source Entity [email protected]
Severity MEDIUM
5.1
Access Vector
N/A
Authentication
N/A
RAW VECTOR AV:N/AC:H/Au:N/C:P/I:P/A:P

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2021-42574 Exploits & PoCs (Proof Of Concept)

GitHub https://github.com/simplylu/CVE-2021-42574
View Code
GitHub https://github.com/maweil/bidi_char_detector
View Code
GitHub https://github.com/tin-z/solidity_CVE-2021-42574-POC
View Code
MODIFIED

Vulnerability data or affected products updated.

PUBLISHED

Vulnerability first announced in NVD.

Attack Vector Matrix

Access Vector NETWORK
Complexity HIGH
Privileges N/A
Interaction REQUIRED
CVSS Vector String CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H

Affected Stack

No specific products linked.