CVE-2021-39197: better_errors is an open source replacement for the standard Rails error page with more information rich error

Q: How do I fix CVE-2021-39197?

better errors: upgrade to 2.8.0. Exact commands for each OS are on this page.

Q: Is CVE-2021-39197 being exploited?

CVE-2021-39197 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-2021-39197 affect?

CVE-2021-39197 affects better errors. Severity is medium (CVSS 6.3). better_errors is an open source replacement for the standard Rails error page with more information rich error pages. It is also usable outside of Rails in any Rack app as Rack middleware. better_errors prior to 2.8.0 did not implement CSRF

Q: How urgent is CVE-2021-39197?

Priority 35/100. No elevated risk signals yet.

Routine

MEDIUM 6.3UPGRADE

CVE-2021-39197 is a medium-severity flaw (CVSS 6.3) affecting better errors. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

better_errors is an open source replacement for the standard Rails error page with more information rich error pages. It is also usable outside of Rails in any Rack app as Rack middleware. better_errors prior to 2.8.0 did not implement CSRF protection for its internal requests. It also did not enforce the correct "Content-Type" header for these requests, which allowed a cross-origin "simple request" to be made without CORS protection. These toget

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.3 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.6% (top 49%)
CISA exploited list	No
Weakness	CWE-352
Published	2021-09-07
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: better errors project

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

Am I affected?

Timeline

2021-09-07 18:15 UTCPublished CVE record published
2026-06-17 04:03 UTCUpdated Record last modified

better errors project better errors UPGRADE

Affected: < 2.8.0

Fixed in: 2.8.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 2.8.0 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade better-errors

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-2021-39197?

better errors: upgrade to 2.8.0. Exact commands for each OS are on this page.

Is CVE-2021-39197 being exploited?

CVE-2021-39197 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-2021-39197 affect?

CVE-2021-39197 affects better errors. Severity is medium (CVSS 6.3). better_errors is an open source replacement for the standard Rails error page with more information rich error pages. It is also usable outside of Rails in any Rack app as Rack middleware. better_errors prior to 2.8.0 did not implement CSRF

How urgent is CVE-2021-39197?

Priority 35/100. No elevated risk signals yet.

Software pages

Ruby on Rails vulnerabilities

References

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