ID CVE-2021-42574
Summary 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.
References
Vulnerable Configurations
  • cpe:2.3:a:unicode:unicode:*:*:*:*:*:*:*:*
    cpe:2.3:a:unicode:unicode:*:*:*:*:*:*:*:*
  • cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
    cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
  • cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
    cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
  • cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
    cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
  • cpe:2.3:a:starwindsoftware:starwind_virtual_san:v8r13:14398:*:*:*:*:*:*
    cpe:2.3:a:starwindsoftware:starwind_virtual_san:v8r13:14398:*:*:*:*:*:*
CVSS
Base: 5.1 (as of 21-03-2024 - 02:40)
Impact:
Exploitability:
CWE CWE-94
CAPEC
  • Code Injection
    An adversary exploits a weakness in input validation on the target to inject new code into that which is currently executing. This differs from code inclusion in that code inclusion involves the addition or replacement of a reference to a code file, which is subsequently loaded by the target and used as part of the code of some application.
  • Leverage Executable Code in Non-Executable Files
    An attack of this type exploits a system's trust in configuration and resource files. When the executable loads the resource (such as an image file or configuration file) the attacker has modified the file to either execute malicious code directly or manipulate the target process (e.g. application server) to execute based on the malicious configuration parameters. Since systems are increasingly interrelated mashing up resources from local and remote sources the possibility of this attack occurring is high.
  • Manipulating User-Controlled Variables
    This attack targets user controlled variables (DEBUG=1, PHP Globals, and So Forth). An attacker can override environment variables leveraging user-supplied, untrusted query variables directly used on the application server without any data sanitization. In extreme cases, the attacker can change variables controlling the business logic of the application. For instance, in languages like PHP, a number of poorly set default configurations may allow the user to override variables.
Access
VectorComplexityAuthentication
NETWORK HIGH NONE
Impact
ConfidentialityIntegrityAvailability
PARTIAL PARTIAL PARTIAL
cvss-vector via4 AV:N/AC:H/Au:N/C:P/I:P/A:P
Last major update 21-03-2024 - 02:40
Published 01-11-2021 - 04:15
Last modified 21-03-2024 - 02:40
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