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CVE-2021-39197

27
FAUCET Score

CVE-2021-39197 affects the better_errors Ruby gem, a development tool for Rails and Rack applications. The vulnerability stems from a lack of CSRF protection and improper Content-Type header enforcement, allowing cross-origin attacks in development environments. With a CVSS score of 8.8 (High), it presents a significant risk (C:H/I:H/A:H) due to its network-based attack vector and low attack complexity, requiring user interaction. There is no evidence of active exploitation, public exploit code, or significant community discussion, and it is not listed in CISA's KEV catalog.

Impacted Technologies

VendorProductVersion(s)CPE
< 2.8.0CPE matchmatch criteria
cpe:2.3:a:better_errors_project:better_errors:*:*:*:*:*:ruby:*:*

CVSS Data

CVSS version used by this source: 3.1

6.3MEDIUM

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
LOW
User Interaction
NONE
Scope
CHANGED
Confidentiality Impact
HIGH
Integrity Impact
NONE
Availability Impact
NONE
Exploitability Score
1.8
Impact Score
4.0
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.64%
Probability of exploitation in next 30 days
EPSS Percentile
46.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0064 is in the 48th percentile among its peer group of 14,875 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.2 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.1 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

github_advisorypatch availablevia nvd_reference
View patch
rubygemspatch availablevia ghsa
Product: better_errorsFixed in: 2.8.0

Vendor Advisories (1)

rubygemsGHSA-w3j4-76qw-wwjmmedium

Older releases of better_errors open to Cross-Site Request Forgery attack

Sep 7, 2021

References

github.com / BetterErrors/better_errors/commit/8e8e796bfbde4aa088741823c8a3fc6df2089bb0
PatchThird Party Advisory
github.com / BetterErrors/better_errors/discussions/507
Third Party Advisory
github.com / BetterErrors/better_errors/pull/474
PatchThird Party Advisory
github.com / BetterErrors/better_errors/security/advisories/GHSA-w3j4-76qw-wwjm
Third Party Advisory