CVE-2021-38196: An issue was discovered in the better-macro crate through 2021-07-22 for Rust

Q: How do I fix CVE-2021-38196?

better-macro: upgrade to newer than 2021-07-22. Exact commands for each OS are on this page.

Q: Is CVE-2021-38196 being exploited?

CVE-2021-38196 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-2021-38196 affect?

CVE-2021-38196 affects better-macro. Severity is critical (CVSS 9.8). An issue was discovered in the better-macro crate through 2021-07-22 for Rust. It intentionally demonstrates that remote attackers can execute arbitrary code via proc-macros, and otherwise has no legitimate purpose.

Q: How urgent is CVE-2021-38196?

Priority 66/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2021-38196 is a critical-severity flaw (CVSS 9.8) affecting better-macro. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in the better-macro crate through 2021-07-22 for Rust. It intentionally demonstrates that remote attackers can execute arbitrary code via proc-macros, and otherwise has no legitimate purpose.

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	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.6% (top 15%)
CISA exploited list	No
Weakness	CWE-94
Published	2021-08-08
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: better-macro project

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

Am I affected?

Timeline

2021-08-08 06:15 UTCPublished CVE record published
2026-06-17 04:01 UTCUpdated Record last modified

better-macro project better-macro UPGRADE

Affected: <= 2021-07-22

Fixed in: newer than 2021-07-22

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy better-macro || rpm -q better-macro || better-macro --version

2. UPGRADE to newer than 2021-07-22 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade better-macro

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade better-macro

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-2021-38196?

better-macro: upgrade to newer than 2021-07-22. Exact commands for each OS are on this page.

Is CVE-2021-38196 being exploited?

CVE-2021-38196 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-2021-38196 affect?

CVE-2021-38196 affects better-macro. Severity is critical (CVSS 9.8). An issue was discovered in the better-macro crate through 2021-07-22 for Rust. It intentionally demonstrates that remote attackers can execute arbitrary code via proc-macros, and otherwise has no legitimate purpose.

How urgent is CVE-2021-38196?

Priority 66/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

References

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