CVE-2021-42574: An issue was discovered in the Bidirectional Algorithm in the Unicode Specification through 14.0

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HIGH 8.3UPGRADEMITIGATEDOWNGRADE

CVE-2021-42574 is a high-severity flaw (CVSS 8.3) affecting unicode, fedora, starwind virtual san. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 invi

Why this priority

High severity
EPSS top 4%: very likely to be exploited
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.3 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	Required
EPSS exploit chance	12.9% (top 4%)
CISA exploited list	No
Weakness	CWE-94
Published	2021-11-01
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: fedoraproject · starwindsoftware · unicode

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-11-01 04:15 UTCPublished CVE record published
2026-06-17 04:09 UTCUpdated Record last modified

unicode unicode UPGRADE

Affected: < 14.0.0

Fixed in: 14.0.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy unicode || rpm -q unicode || unicode --version

2. UPGRADE to 14.0.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade unicode

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade unicode

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

fedoraproject fedora MITIGATE

Affected: 33 · 34 · 35

Fixed in: no fixed release known

Safe to downgrade to: a release before 33

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

starwindsoftware starwind virtual san DOWNGRADE

Affected: v8r13 14398

Fixed in: no fixed release known

Safe to downgrade to: a release before v8r13

1. Check installed version

apt-cache policy starwind-virtual-san || rpm -q starwind-virtual-san || starwind-virtual-san --version

2. No fixed release: DOWNGRADE to a release before v8r13 (Debian / Ubuntu)

apt-cache madison starwind-virtual-san sudo apt install starwind-virtual-san=<VERSION_BEFORE_v8r13> sudo apt-mark hold starwind-virtual-san

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list starwind-virtual-san sudo dnf downgrade starwind-virtual-san-<VERSION_BEFORE_v8r13> sudo dnf versionlock add starwind-virtual-san

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-42574?

unicode: upgrade to 14.0.0; fedora: mitigate or apply the listed mitigation; starwind virtual san: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-42574 being exploited?

CVE-2021-42574 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-42574 affect?

CVE-2021-42574 affects unicode, fedora, starwind virtual san. Severity is high (CVSS 8.3). 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

How urgent is CVE-2021-42574?

Priority 58/100. High severity; EPSS top 4%: very likely to be exploited; Public exploit reference

Related CVEs

CVE-2021-42694 HIGH 8.3 UPGRADE An issue was discovered in the character definitions of the Unicode Specification through 14.0

References

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