CVE-2021-42574
Oracle Unicode Bidirectional Algorithm Code Injection Vulnerability
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.
INFO
Published Date :
Nov. 1, 2021, 4:15 a.m.
Last Modified :
June 17, 2026, 4:09 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2021-42574
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 2.0 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | HIGH | [email protected] |
Solution
- Update all affected packages to resolve the vulnerability.
- For Nutanix, upgrade AOS and AHV software as recommended.
- For GitLab, upgrade to a patched version or later.
- For ZTE CGSL, contact vendor for updated packages.
Public PoC/Exploit Available at Github
CVE-2021-42574 has a 107 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2021-42574.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2021-42574 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2021-42574
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Catches hidden and invisible-unicode instructions smuggled into AI coding-agent config and skill files. Zero-config CI check.
ai-agents claude cli cursor developer-tools github-copilot homoglyph invisible-unicode llm mcp prompt-injection rules-file-backdoor sarif security static-analysis supply-chain-security trojan-source zero-width
JavaScript TypeScript
See the invisible reason two strings won't compare equal — codepoint diff + 10-fold equality matrix + homoglyph/bidi security flags. 100% in your browser, view-source verifiable.
devtools homoglyph javascript local-first privacy security unicode web-tool
JavaScript HTML CSS
None
Python Dockerfile Shell
An advisory inspection service that reads text and documents leaving a secure network and flags content that should not be allowed to go.
Python JavaScript CSS HTML Shell
Extraction-time data falsification against LLM document/email pipelines: cached-value XLSX & MIME-multipart divergence, with detectors. Sequel to lying-spreadsheets.
Python Shell
None
Shell Rust Python Lua TypeScript
Dr. Dreamers Mark Down Reader for MacOS
Makefile Rust
Claude Code skill that audits any third-party repo (skill, plugin, npm/PyPI package) for supply-chain safety before installing. Prompt-injection pre-flight + 5-category framework + Python-layer behavioral sandbox + Trojan Source scanner. Stdlib-only, zero runtime deps.
Python
A command-line tool that detects and fixes common text encoding problems in a repository.
code-quality code-quality-checker command-line-tool formatter
Go Makefile
Detect homoglyph / Unicode-confusable attacks in online gambling SEO spam (JuD0L).
Python YARA HTML
None
TypeScript JavaScript
Enforcement determinístico contra malware de supply-chain e abuso de agentes LLM em ambientes de desenvolvimento.
Rust Makefile Shell HTML CSS JavaScript
Reveal & remove invisible, dangerous & confusable characters in your text — zero-width spaces, BOMs, bidi (Trojan Source), homoglyphs, smart quotes. 100% local. Web app + library + CLI.
homoglyph invisible-characters prompt-injection security smart-quotes text-cleaner trojan-source unicode zero-dependency zero-width-space
JavaScript TypeScript HTML CSS
Free, offline, AGPL-3.0 audit skill — detects poisoned Claude Code skills + repo AI-config files before your AI reads them. Covers TrapDoor + Shai-Hulud attack surface.
System-level protection against malicious git repositories
Makefile Go Shell
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2021-42574 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2021-42574 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 17, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2021-42574', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2024-06-11T15:16:49.504878Z'} -
CVE Modified by [email protected]
Jun. 17, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'n/a', 'product': 'n/a', 'versions': [{'status': 'affected', 'version': 'n/a'}]}] -
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Nov. 21, 2024
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 [email protected]
Aug. 04, 2024
Action Type Old Value New Value -
CVE Modified by [email protected]
Jun. 11, 2024
Action Type Old Value New Value -
CVE Modified by [email protected]
May. 17, 2024
Action Type Old Value New Value -
CVE Modified by [email protected]
May. 14, 2024
Action Type Old Value New Value -
CVE Modified by [email protected]
Apr. 11, 2024
Action Type Old Value New Value -
CVE Modified by [email protected]
Mar. 21, 2024
Action Type Old Value New Value Added Tag MITRE disputed -
CVE Modified by [email protected]
Nov. 07, 2023
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/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ [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/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ [No types assigned] Removed Reference MITRE https://lists.fedoraproject.org/archives/list/[email protected]/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ 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/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ -
Modified Analysis by [email protected]
Oct. 25, 2022
Action Type Old Value New Value 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 Added CPE Configuration OR *cpe:2.3:a:starwindsoftware:starwind_virtual_san:v8r13:14398:*:*:*:*:*:* -
CVE Modified by [email protected]
Oct. 16, 2022
Action Type Old Value New Value Added Reference https://security.gentoo.org/glsa/202210-09 [No Types Assigned] -
CVE Modified by [email protected]
Oct. 11, 2022
Action Type Old Value New Value Added Reference https://www.starwindsoftware.com/security/sw-20220804-0002/ [No Types Assigned] -
Modified Analysis by [email protected]
Sep. 03, 2022
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 [email protected]
May. 12, 2022
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/tr36/ [No Types Assigned] Added Reference https://www.unicode.org/reports/tr9/tr9-44.html#HL4 [No Types Assigned] Added Reference https://www.unicode.org/reports/tr31/ [No Types Assigned] Added Reference https://www.unicode.org/reports/tr39/ [No Types Assigned] -
Modified Analysis by [email protected]
Nov. 30, 2021
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 [email protected]
Nov. 26, 2021
Action Type Old Value New Value Added Reference https://www.scyon.nl/post/trojans-in-your-source-code [No Types Assigned] -
Modified Analysis by [email protected]
Nov. 16, 2021
Action Type Old Value New Value Added CVSS V2 Metadata Victim must voluntarily interact with attack mechanism Removed CVSS V2 NIST (AV:N/AC:L/Au:N/C:P/I:P/A:P) Added CVSS V2 NIST (AV:N/AC:H/Au:N/C:P/I:P/A:P) Removed CVSS V3.1 NIST AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Added CVSS V3.1 NIST AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H 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 CPE Configuration OR *cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* *cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:* *cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:* -
CVE Modified by [email protected]
Nov. 11, 2021
Action Type Old Value New Value Added Reference https://lists.fedoraproject.org/archives/list/[email protected]/message/IH2RG5YTR6ZZOLUV3EUPZEIJR7XHJLVD/ [No Types Assigned] -
CVE Modified by [email protected]
Nov. 09, 2021
Action Type Old Value New Value Added Reference https://www.kb.cert.org/vuls/id/999008 [No Types Assigned] -
CVE Modified by [email protected]
Nov. 05, 2021
Action Type Old Value New Value Added Reference https://lists.fedoraproject.org/archives/list/[email protected]/message/LQNTFF24ROHLVPLUOEISBN3F7QM27L4U/ [No Types Assigned] -
CVE Modified by [email protected]
Nov. 04, 2021
Action Type Old Value New Value Added Reference https://lists.fedoraproject.org/archives/list/[email protected]/message/QUPA37D57VPTDLSXOOGF4UXUEADOC4PQ/ [No Types Assigned] -
CVE Modified by [email protected]
Nov. 03, 2021
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 [email protected]
Nov. 02, 2021
Action Type Old Value New Value Added CVSS V2 NIST (AV:N/AC:L/Au:N/C:P/I:P/A:P) Added CVSS V3.1 NIST AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H 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 Added CWE NIST CWE-94 Added CPE Configuration OR *cpe:2.3:a:unicode:unicode:*:*:*:*:*:*:*:* versions up to (excluding) 14.0.0 -
CVE Modified by [email protected]
Nov. 01, 2021
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 [email protected]
Nov. 01, 2021
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 [email protected]
Nov. 01, 2021
Action Type Old Value New Value Added Reference http://www.openwall.com/lists/oss-security/2021/11/01/1 [No Types Assigned]