dbcve.org
FedoraOperating system · Fedoraproject

CVE-2021-42574

HIGH · 8.3 CVSS v3.1 Published 2021-11-01
Fix available
A fix is available. Upgrade to 14.0.0 or later.
See remediation →
90/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-94

The application evaluates attacker-influenced input as code, handing them a way to run logic inside the process. Depending on the runtime this can escalate directly to remote code execution. Remediation means removing dynamic evaluation of untrusted input and replacing it with safe, data-driven alternatives.

General guidance for the code injection class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FedoraOperating system
Affected:= 33= 34= 35
UnicodeApplication
Affected:< 14.0.0
Starwind Virtual SanApplication
Affected:= v8r13

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 14.0.0 or later
Fixed in 14.0.0
Recommended fix Moderate confidence

Unicode 14.0.0 or later for the specification; Fedora 36+ for Fedora systems

  1. For Fedora systems: Upgrade to a supported Fedora version (Fedora 36 or later) which includes compilers and tooling with BIDI attack mitigations
  2. Verify that all compiler toolchains (gcc, clang, etc.) are updated to versions that implement Unicode Security Considerations (UAX #31, UTS #39)
  3. For Starwind Virtual San v8r13: Contact vendor for compiler/tooling updates that address BIDI vulnerabilities in any bundled or integrated development tools
  4. Review codebase for any hardcoded Unicode character handling and ensure tools process UAX #31 identifier rules
  5. Enable any available compiler flags that detect or warn about potentially dangerous bidirectional character sequences in source code
Caveat Minimal - this is a specification/coding practice fix; verify custom code doesn't rely on BIDI characters in identifiers

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-42574 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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