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URL: https://nvd.nist.gov/vuln/detail/CVE-2021-42574

⇱ NVD - CVE-2021-42574

  1. Vulnerabilities

CVE-2021-42574 Detail

Disputed     

Modified After Enrichment

This CVE record has been updated after NVD enrichment efforts were completed. Enrichment data supplied by the NVD may require amendment due to these changes.

Current Description

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.


View Analysis Description

Analysis 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.

Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NVD assessment not yet provided.

References to Advisories, Solutions, and Tools

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URL Source(s) Tag(s)
http://www.openwall.com/lists/oss-security/2021/11/01/1 CVE, MITRE Exploit  Mailing List  Mitigation  Third Party Advisory 
http://www.openwall.com/lists/oss-security/2021/11/01/4 CVE, MITRE Exploit  Mailing List  Third Party Advisory 
http://www.openwall.com/lists/oss-security/2021/11/01/5 CVE, MITRE Mailing List  Third Party Advisory 
http://www.openwall.com/lists/oss-security/2021/11/01/6 CVE, MITRE Mailing List  Third Party Advisory 
http://www.openwall.com/lists/oss-security/2021/11/02/10 CVE, MITRE Mailing List 
http://www.unicode.org/versions/Unicode14.0.0/ CVE, MITRE Release Notes  Vendor Advisory 
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ CVE, MITRE
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ CVE, MITRE
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ CVE, MITRE
https://security.gentoo.org/glsa/202210-09 CVE, MITRE Third Party Advisory 
https://trojansource.codes CVE, MITRE Exploit  Technical Description  Third Party Advisory 
https://www.kb.cert.org/vuls/id/999008 CVE, MITRE Third Party Advisory  US Government Resource 
https://www.scyon.nl/post/trojans-in-your-source-code CVE, MITRE Exploit  Mitigation  Third Party Advisory 
https://www.starwindsoftware.com/security/sw-20220804-0002/ CVE, MITRE Third Party Advisory 
https://www.unicode.org/reports/tr31/ CVE, MITRE Technical Description  Vendor Advisory 
https://www.unicode.org/reports/tr36/ CVE, MITRE Technical Description  Vendor Advisory 
https://www.unicode.org/reports/tr39/ CVE, MITRE Technical Description  Vendor Advisory 
https://www.unicode.org/reports/tr9/tr9-44.html#HL4 CVE, MITRE Technical Description  Vendor Advisory 

Weakness Enumeration

CWE-ID CWE Name Source
CWE-94 Improper Control of Generation of Code ('Code Injection') 👁 cwe source acceptance level
NIST  

Known Affected Software Configurations Switch to CPE 2.2

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Denotes Vulnerable Software
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Change History

27 change records found show changes

CVE Modified by CISA-ADP 6/17/2026 12:09:50 AM

Action Type Old Value New Value
Added SSVC 
{"timestamp":"2024-06-11T15:16:49.504878Z","id":"CVE-2021-42574","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}

CVE Modified by MITRE 6/17/2026 12:09:50 AM

Action Type Old Value New Value
Added Affected 
[{"vendor":"n/a","product":"n/a","versions":[{"version":"n/a","status":"affected"}]}]

CVE Modified by CVE 11/21/2024 1:27:50 AM

Action Type Old Value New Value
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/01/1
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/01/4
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/01/5
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/01/6
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/02/10
Added Reference 
http://www.unicode.org/versions/Unicode14.0.0/
Added Reference 
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/
Added Reference 
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/
Added Reference 
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/
Added Reference 
https://security.gentoo.org/glsa/202210-09
Added Reference 
https://trojansource.codes
Added Reference 
https://www.kb.cert.org/vuls/id/999008
Added Reference 
https://www.scyon.nl/post/trojans-in-your-source-code
Added Reference 
https://www.starwindsoftware.com/security/sw-20220804-0002/
Added Reference 
https://www.unicode.org/reports/tr31/
Added Reference 
https://www.unicode.org/reports/tr36/
Added Reference 
https://www.unicode.org/reports/tr39/
Added Reference 
https://www.unicode.org/reports/tr9/tr9-44.html#HL4

CVE Modified by MITRE 8/04/2024 12:16:04 AM

Action Type Old Value New Value

CVE Modified by MITRE 6/11/2024 12:15:15 PM

Action Type Old Value New Value

CVE Modified by MITRE 5/16/2024 10:01:34 PM

Action Type Old Value New Value

CVE Modified by MITRE 5/14/2024 5:30:41 AM

Action Type Old Value New Value

CVE Modified by MITRE 4/10/2024 9:13:06 PM

Action Type Old Value New Value

CVE Modified by MITRE 3/20/2024 10:40:42 PM

Action Type Old Value New Value
Added Tag 
MITRE disputed

CVE Modified by MITRE 11/06/2023 10:39:12 PM

Action Type Old Value New Value
Changed 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.


 
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.
Added Reference 
MITRE https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ [No types assigned]
Added Reference 
MITRE https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ [No types assigned]
Added Reference 
MITRE https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ [No types assigned]
Removed Reference 
MITRE https://lists.fedoraproject.org/archives/list/[email protected]/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/
Removed Reference 
MITRE https://lists.fedoraproject.org/archives/list/[email protected]/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/
Removed Reference 
MITRE https://lists.fedoraproject.org/archives/list/[email protected]/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/

Modified Analysis by NIST 10/25/2022 12:38:28 PM

Action Type Old Value New Value
Added CPE Configuration 
OR
 *cpe:2.3:a:starwindsoftware:starwind_virtual_san:v8r13:14398:*:*:*:*:*:*
Changed Reference Type 
https://security.gentoo.org/glsa/202210-09 No Types Assigned


 
https://security.gentoo.org/glsa/202210-09 Third Party Advisory
Changed Reference Type 
https://www.starwindsoftware.com/security/sw-20220804-0002/ No Types Assigned


 
https://www.starwindsoftware.com/security/sw-20220804-0002/ Third Party Advisory

CVE Modified by MITRE 10/16/2022 1:15:13 PM

Action Type Old Value New Value
Added Reference 
https://security.gentoo.org/glsa/202210-09 [No Types Assigned]

CVE Modified by MITRE 10/11/2022 6:15:11 PM

Action Type Old Value New Value
Added Reference 
https://www.starwindsoftware.com/security/sw-20220804-0002/ [No Types Assigned]

Modified Analysis by NIST 9/02/2022 11:59:28 PM

Action Type Old Value New Value
Changed Reference Type 
https://www.unicode.org/reports/tr31/ No Types Assigned


 
https://www.unicode.org/reports/tr31/ Technical Description, Vendor Advisory
Changed Reference Type 
https://www.unicode.org/reports/tr36/ No Types Assigned


 
https://www.unicode.org/reports/tr36/ Technical Description, Vendor Advisory
Changed Reference Type 
https://www.unicode.org/reports/tr39/ No Types Assigned


 
https://www.unicode.org/reports/tr39/ Technical Description, Vendor Advisory
Changed Reference Type 
https://www.unicode.org/reports/tr9/tr9-44.html#HL4 No Types Assigned


 
https://www.unicode.org/reports/tr9/tr9-44.html#HL4 Technical Description, Vendor Advisory

CVE Modified by MITRE 5/12/2022 11:15:07 AM

Action Type Old Value New Value
Changed Description 
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.


 
** 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.
Added Reference 
https://www.unicode.org/reports/tr31/ [No Types Assigned]
Added Reference 
https://www.unicode.org/reports/tr36/ [No Types Assigned]
Added Reference 
https://www.unicode.org/reports/tr39/ [No Types Assigned]
Added Reference 
https://www.unicode.org/reports/tr9/tr9-44.html#HL4 [No Types Assigned]

Modified Analysis by NIST 11/30/2021 3:22:29 PM

Action Type Old Value New Value
Changed Reference Type 
https://www.scyon.nl/post/trojans-in-your-source-code No Types Assigned


 
https://www.scyon.nl/post/trojans-in-your-source-code Exploit, Mitigation, Third Party Advisory

CVE Modified by MITRE 11/26/2021 9:15:07 AM

Action Type Old Value New Value
Added Reference 
https://www.scyon.nl/post/trojans-in-your-source-code [No Types Assigned]

Modified Analysis by NIST 11/16/2021 10:16:57 AM

Action Type Old Value New Value
Added CVSS V3.1 
NIST AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H
Removed CVSS V3.1 
NIST AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Added CVSS V2 
NIST (AV:N/AC:H/Au:N/C:P/I:P/A:P)
Removed CVSS V2 
NIST (AV:N/AC:L/Au:N/C:P/I:P/A:P)
Added CPE Configuration 
OR
 *cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
 *cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
 *cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
Changed Reference Type 
http://www.openwall.com/lists/oss-security/2021/11/02/10 No Types Assigned


 
http://www.openwall.com/lists/oss-security/2021/11/02/10 Mailing List
Changed Reference Type 
https://lists.fedoraproject.org/archives/list/[email protected]/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ No Types Assigned


 
https://lists.fedoraproject.org/archives/list/[email protected]/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ Mailing List, Third Party Advisory
Changed Reference Type 
https://lists.fedoraproject.org/archives/list/[email protected]/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ No Types Assigned


 
https://lists.fedoraproject.org/archives/list/[email protected]/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ Mailing List, Third Party Advisory
Changed Reference Type 
https://lists.fedoraproject.org/archives/list/[email protected]/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ No Types Assigned


 
https://lists.fedoraproject.org/archives/list/[email protected]/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ Mailing List, Third Party Advisory
Changed Reference Type 
https://www.kb.cert.org/vuls/id/999008 No Types Assigned


 
https://www.kb.cert.org/vuls/id/999008 Third Party Advisory, US Government Resource
Added CVSS V2 Metadata 
Victim must voluntarily interact with attack mechanism

CVE Modified by MITRE 11/10/2021 10:15:07 PM

Action Type Old Value New Value
Added Reference 
https://lists.fedoraproject.org/archives/list/[email protected]/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ [No Types Assigned]

CVE Modified by MITRE 11/09/2021 1:15:07 PM

Action Type Old Value New Value
Added Reference 
https://www.kb.cert.org/vuls/id/999008 [No Types Assigned]

CVE Modified by MITRE 11/05/2021 12:15:16 AM

Action Type Old Value New Value
Added Reference 
https://lists.fedoraproject.org/archives/list/[email protected]/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ [No Types Assigned]

CVE Modified by MITRE 11/04/2021 12:15:12 AM

Action Type Old Value New Value
Added Reference 
https://lists.fedoraproject.org/archives/list/[email protected]/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ [No Types Assigned]

CVE Modified by MITRE 11/02/2021 8:15:08 PM

Action Type Old Value New Value
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/02/10 [No Types Assigned]

Initial Analysis by NIST 11/02/2021 2:43:39 PM

Action Type Old Value New Value
Added CVSS V3.1 
NIST AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Added CVSS V2 
NIST (AV:N/AC:L/Au:N/C:P/I:P/A:P)
Added CWE 
NIST CWE-94
Added CPE Configuration 
OR
 *cpe:2.3:a:unicode:unicode:*:*:*:*:*:*:*:* versions up to (excluding) 14.0.0
Changed Reference Type 
http://www.openwall.com/lists/oss-security/2021/11/01/1 No Types Assigned


 
http://www.openwall.com/lists/oss-security/2021/11/01/1 Exploit, Mailing List, Mitigation, Third Party Advisory
Changed Reference Type 
http://www.openwall.com/lists/oss-security/2021/11/01/4 No Types Assigned


 
http://www.openwall.com/lists/oss-security/2021/11/01/4 Exploit, Mailing List, Third Party Advisory
Changed Reference Type 
http://www.openwall.com/lists/oss-security/2021/11/01/5 No Types Assigned


 
http://www.openwall.com/lists/oss-security/2021/11/01/5 Mailing List, Third Party Advisory
Changed Reference Type 
http://www.openwall.com/lists/oss-security/2021/11/01/6 No Types Assigned


 
http://www.openwall.com/lists/oss-security/2021/11/01/6 Mailing List, Third Party Advisory
Changed Reference Type 
http://www.unicode.org/versions/Unicode14.0.0/ No Types Assigned


 
http://www.unicode.org/versions/Unicode14.0.0/ Release Notes, Vendor Advisory
Changed Reference Type 
https://trojansource.codes No Types Assigned


 
https://trojansource.codes Exploit, Technical Description, Third Party Advisory

CVE Modified by MITRE 11/01/2021 5:15:08 PM

Action Type Old Value New Value
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/01/5 [No Types Assigned]
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/01/6 [No Types Assigned]

CVE Modified by MITRE 11/01/2021 2:15:08 PM

Action Type Old Value New Value
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/01/4 [No Types Assigned]

CVE Modified by MITRE 11/01/2021 5:15:09 AM

Action Type Old Value New Value
Added Reference 
http://www.openwall.com/lists/oss-security/2021/11/01/1 [No Types Assigned]

Quick Info

CVE Dictionary Entry:
CVE-2021-42574
NVD Published Date:
11/01/2021
NVD Last Modified:
06/17/2026
Source:
MITRE