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 together left an application with better_errors enabled open to cross-origin attacks. As a developer tool, better_errors documentation strongly recommends addition only to the `development` bundle group, so this vulnerability should only affect development environments. Please ensure that your project limits better_errors to the `development` group (or the non-Rails equivalent). Starting with release 2.8.x, CSRF protection is enforced. It is recommended that you upgrade to the latest release, or minimally to "~> 2.8.3". There are no known workarounds to mitigate the risk of using older releases of better_errors.
Published 2021-09-07 18:15:07
Updated 2021-09-14 18:34:34
Source GitHub, Inc.
View at NVD,   CVE.org
Vulnerability category: Cross-site request forgery (CSRF)

Exploit prediction scoring system (EPSS) score for CVE-2021-39197

0.13%
Probability of exploitation activity in the next 30 days EPSS Score History
~ 47 %
Percentile, the proportion of vulnerabilities that are scored at or less

CVSS scores for CVE-2021-39197

Base Score Base Severity CVSS Vector Exploitability Score Impact Score Score Source First Seen
6.8
MEDIUM AV:N/AC:M/Au:N/C:P/I:P/A:P
8.6
6.4
NIST
8.8
HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
2.8
5.9
NIST
6.3
MEDIUM CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N
1.8
4.0
GitHub, Inc.

CWE ids for CVE-2021-39197

  • The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request.
    Assigned by: security-advisories@github.com (Primary)

References for CVE-2021-39197

Products affected by CVE-2021-39197

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