CVE-2021-42574
environment: Unicode's bidirectional (BiDi) override characters can cause trojan source attacks
Severity
ModerateRed Hat Product Security
CVSS 3.1
Review impact separately from score.
Published · November 1, 2021
Updated · August 7, 2026
Description
A flaw was found in the way Unicode standards are implemented in the context of development environments, which have specialized requirements for rendering text. An attacker could exploit this to deceive a human reviewer by creating a malicious patch containing well placed BiDi characters. The special handling and rendering of those characters can be then used in an attempt to hide unexpected and potentially dangerous behaviour from the reviewer.
Statement
This is a flaw with the way Unicode standards are implemented in the context of development environments, which have specialized requirements for rendering text. This is not a flaw in Red Hat products.
CVSS score applicability
The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.
Mitigation
This issue can be mitigated by ensuring code commits get a proper review. All new commits can also be scanned for the presence of BiDi characters before accepting the commit.
CVSS / CWE
CVSS 3.1 · 8.5CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
CWE-838 · Inappropriate Encoding for Output Context