CVE-2021-39197
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.64%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- EPSS
- 0.64% probability · 49th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-352
- Affected
- better errors project/better errors
- Source
- security-advisories@github.com
References
- https://github.com/BetterErrors/better_errors/commit/8e8e796bfbde4aa088741823c8a3fc6df2089bb0Patch, Third Party Advisory
- https://github.com/BetterErrors/better_errors/discussions/507Third Party Advisory
- https://github.com/BetterErrors/better_errors/pull/474Patch, Third Party Advisory
- https://github.com/BetterErrors/better_errors/security/advisories/GHSA-w3j4-76qw-wwjmThird Party Advisory
- https://github.com/BetterErrors/better_errors/commit/8e8e796bfbde4aa088741823c8a3fc6df2089bb0Patch, Third Party Advisory
- https://github.com/BetterErrors/better_errors/discussions/507Third Party Advisory
- https://github.com/BetterErrors/better_errors/pull/474Patch, Third Party Advisory
- https://github.com/BetterErrors/better_errors/security/advisories/GHSA-w3j4-76qw-wwjmThird Party Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.