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Vulnerability Details : CVE-2021-42574

** 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.
Publish Date : 2021-11-01 Last Update Date : 2022-05-12
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- CVSS Scores & Vulnerability Types

CVSS Score
Confidentiality Impact Partial (There is considerable informational disclosure.)
Integrity Impact Partial (Modification of some system files or information is possible, but the attacker does not have control over what can be modified, or the scope of what the attacker can affect is limited.)
Availability Impact Partial (There is reduced performance or interruptions in resource availability.)
Access Complexity High (Specialized access conditions exist. It is hard to exploit and several special conditions must be satisfied to exploit)
Authentication Not required (Authentication is not required to exploit the vulnerability.)
Gained Access None
Vulnerability Type(s)

- Related OVAL Definitions

Title Definition Id Class Family
RHSA-2021:4033: binutils security update (Moderate) oval:com.redhat.rhsa:def:20214033 unix
RHSA-2021:4585: gcc-toolset-10-gcc security update (Moderate) oval:com.redhat.rhsa:def:20214585 unix
RHSA-2021:4586: gcc-toolset-11-gcc security update (Moderate) oval:com.redhat.rhsa:def:20214586 unix
RHSA-2021:4587: gcc security update (Moderate) oval:com.redhat.rhsa:def:20214587 unix
RHSA-2021:4590: rust-toolset:rhel8 security update (Moderate) oval:com.redhat.rhsa:def:20214590 unix
RHSA-2021:4591: gcc-toolset-11-annobin security update (Moderate) oval:com.redhat.rhsa:def:20214591 unix
RHSA-2021:4592: gcc-toolset-10-annobin security update (Moderate) oval:com.redhat.rhsa:def:20214592 unix
RHSA-2021:4593: annobin security update (Moderate) oval:com.redhat.rhsa:def:20214593 unix
RHSA-2021:4594: gcc-toolset-11-binutils security update (Moderate) oval:com.redhat.rhsa:def:20214594 unix
RHSA-2021:4595: binutils security update (Moderate) oval:com.redhat.rhsa:def:20214595 unix
RHSA-2021:4649: gcc-toolset-10-binutils security update (Moderate) oval:com.redhat.rhsa:def:20214649 unix
RHSA-2021:4743: llvm-toolset:rhel8 security update (Moderate) oval:com.redhat.rhsa:def:20214743 unix
OVAL (Open Vulnerability and Assessment Language) definitions define exactly what should be done to verify a vulnerability or a missing patch. Check out the OVAL definitions if you want to learn what you should do to verify a vulnerability.

- Products Affected By CVE-2021-42574

# Product Type Vendor Product Version Update Edition Language
1 OS Fedoraproject Fedora 33 * * * Version Details Vulnerabilities
2 OS Fedoraproject Fedora 34 * * * Version Details Vulnerabilities
3 OS Fedoraproject Fedora 35 * * * Version Details Vulnerabilities
4 Application Unicode Unicode * * * * Version Details Vulnerabilities

- Number Of Affected Versions By Product

Vendor Product Vulnerable Versions
Fedoraproject Fedora 3
Unicode Unicode 1

- References For CVE-2021-42574
MLIST [oss-security] 20211102 Re: CVE-2021-42574: rustc 1.56.0 and bidirectional-override codepoints in source code
MLIST [oss-security] 20211101 CVE-2021-42574: rustc 1.56.0 and bidirectional-override codepoints in source code
FEDORA FEDORA-2021-0578e23912
CERT-VN VU#999008
MLIST [oss-security] 20211102 Re: Trojan Source Attacks
FEDORA FEDORA-2021-7ad3a01f6a
MLIST [oss-security] 20211101 Trojan Source Attacks
MLIST [oss-security] 20211101 Re: CVE-2021-42574: rustc 1.56.0 and bidirectional-override codepoints in source code
FEDORA FEDORA-2021-443139f67c

- Metasploit Modules Related To CVE-2021-42574

There are not any metasploit modules related to this CVE entry (Please visit for more information)

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