CVE-2021-4238: Randomly-generated alphanumeric strings contain significantly less entropy than expected

Q: How do I fix CVE-2021-4238?

goutils: upgrade to 1.1.1. Exact commands for each OS are on this page.

Q: Is CVE-2021-4238 being exploited?

CVE-2021-4238 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-4238 affect?

CVE-2021-4238 affects goutils. Severity is critical (CVSS 9.1). Randomly-generated alphanumeric strings contain significantly less entropy than expected. The RandomAlphaNumeric and CryptoRandomAlphaNumeric functions always return strings containing at least one digit from 0 to 9. This significantly redu

Q: How urgent is CVE-2021-4238?

Priority 60/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.1REMOTEUPGRADE

CVE-2021-4238 is a critical-severity flaw (CVSS 9.1) affecting goutils. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Randomly-generated alphanumeric strings contain significantly less entropy than expected. The RandomAlphaNumeric and CryptoRandomAlphaNumeric functions always return strings containing at least one digit from 0 to 9. This significantly reduces the amount of entropy in short strings generated by these functions.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.4% (top 27%)
CISA exploited list	No
Weakness	CWE-331
Published	2022-12-27
Last modified	2026-06-17

Publisher (CNA): Go Project · Vendor: goutils project

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

Am I affected?

Timeline

2022-12-27 22:15 UTCPublished CVE record published
2026-06-17 04:19 UTCUpdated Record last modified

goutils project goutils UPGRADE

Affected: < 1.1.1

Fixed in: 1.1.1

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 1.1.1 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade goutils

Note

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

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-2021-4238?

goutils: upgrade to 1.1.1. Exact commands for each OS are on this page.

Is CVE-2021-4238 being exploited?

CVE-2021-4238 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-2021-4238 affect?

CVE-2021-4238 affects goutils. Severity is critical (CVSS 9.1). Randomly-generated alphanumeric strings contain significantly less entropy than expected. The RandomAlphaNumeric and CryptoRandomAlphaNumeric functions always return strings containing at least one digit from 0 to 9. This significantly redu

How urgent is CVE-2021-4238?

Priority 60/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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