{"id":"CVE-2021-39197","aliases":["EUVD-2021-2122","GHSA-w3j4-76qw-wwjm"],"status":"published","title":"Cross-Site Request Forgery in better_errors","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 \"~\u003e 2.8.3\". There are no known workarounds to mitigate the risk of using older releases of better_errors.","severity":{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00641,"percentile":0.51232,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-352"],"published":"2021-09-07T17:30:11Z","modified":"2026-10-20T10:54:53Z","fixes":[{"ecosystem":"RubyGems","package":"better_errors","fixed_in":["2.8.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"RubyGems","package":"better_errors","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.8.0"}]}]},{"source":"osv","ecosystem":"RubyGems","package":"better_errors","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.8.0"}]}],"versions":["0.0.1","0.0.2","0.0.3","0.0.4","0.0.5","0.0.6","0.0.7","0.0.8","0.1.0","0.1.1","0.2.0","0.3.0","0.3.2","0.5.0","0.6.0","0.7.0","0.7.2","0.8.0","0.9.0","1.0.0","1.0.0.rc1","1.0.1","1.1.0","2.0.0","2.1.0","2.1.1","2.2.0","2.3.0","2.4.0","2.5.0","2.5.1","2.6.0","2.7.0","2.7.1"]}],"products":[{"vendor":"better_errors_project","product":"better_errors"},{"vendor":"bettererrors","product":"better_errors"}],"references":[{"url":"https://github.com/BetterErrors/better_errors/security/advisories/GHSA-w3j4-76qw-wwjm","tags":["x_refsource_CONFIRM","x_transferred","Third Party Advisory","advisory","web"]},{"url":"https://github.com/BetterErrors/better_errors/pull/474","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web"]},{"url":"https://github.com/BetterErrors/better_errors/commit/8e8e796bfbde4aa088741823c8a3fc6df2089bb0","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web"]},{"url":"https://github.com/BetterErrors/better_errors/discussions/507","tags":["x_refsource_MISC","x_transferred","Third Party Advisory","advisory","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-39197","tags":["advisory"]},{"url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/better_errors/CVE-2021-39197.yml","tags":["web"]},{"url":"https://github.com/advisories/GHSA-w3j4-76qw-wwjm"},{"url":"https://github.com/BetterErrors/better_errors","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2021-39197","title":"Cross-Site Request Forgery in better_errors","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 \"~\u003e 2.8.3\". There are no known workarounds to mitigate the risk of using older releases of better_errors.","status":"published","published":"2021-09-07T17:30:11Z","modified":"2024-08-04T01:58:18.263Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-352"],"updated_at":"2026-11-02T14:33:09.175141Z"}],"euvd":[{"id":"EUVD-2021-2122","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 \"~\u003e 2.8.3\". There are no known workarounds to mitigate the risk of using older releases of better_errors.","status":"published","published":"2021-09-07T17:30:11Z","modified":"2024-08-04T01:58:18Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N","level":"medium"}],"updated_at":"2026-11-03T03:24:24.305495Z"}],"ghsa":[{"id":"GHSA-w3j4-76qw-wwjm","title":"Older releases of better_errors open to Cross-Site Request Forgery attack","description":"### Impact\nbetter_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.\n\n_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)._\n\n### Patches\nStarting with release 2.8.x, CSRF protection is enforced. It is recommended that you upgrade to the latest release, or minimally to \"~\u003e 2.8.3\".\n\n### Workarounds\nThere are no known workarounds to mitigate the risk of using older releases of better_errors.\n\n### References\n- Chris Moberly provided [an example attack that uses a now-patched vulnerability of webpack-dev-server in conjunction with Better Errors](https://about.gitlab.com/blog/2021/09/07/why-are-developers-vulnerable-to-driveby-attacks/)\n\n### For more information\nIf you have any questions or comments about this advisory, please\n- Add to the [discussion in better_errors](https://github.com/BetterErrors/better_errors/discussions/507)\n- Open an issue in [better_errors](https://github.com/BetterErrors/better_errors)\n","status":"published","published":"2021-09-07T23:08:24Z","modified":"2023-05-04T19:34:08Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N","level":"medium"}],"cwes":["CWE-352"],"updated_at":"2026-11-02T14:36:52.310293Z"}],"nvd":[{"id":"CVE-2021-39197","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 \"~\u003e 2.8.3\". There are no known workarounds to mitigate the risk of using older releases of better_errors.","status":"published","published":"2021-09-07T18:15:07.473Z","modified":"2026-06-17T04:03:17.597Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N","level":"medium","assessor":"secondary"},{"version":"3.1","score":8.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high","assessor":"primary"},{"version":"2.0","score":6.8,"vector":"AV:N/AC:M/Au:N/C:P/I:P/A:P","level":"medium","assessor":"primary"}],"cwes":["CWE-352"],"updated_at":"2026-11-02T14:06:58.05696Z"}],"osv":[{"id":"CVE-2021-39197","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 \"~\u003e 2.8.3\". There are no known workarounds to mitigate the risk of using older releases of better_errors.","status":"published","published":"2021-09-07T18:15:07.473Z","modified":"2026-10-20T10:54:53.779027512Z","cvss":[{"version":"3.1","score":8.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","level":"high"}],"updated_at":"2026-11-02T15:44:20.843843Z"},{"id":"GHSA-w3j4-76qw-wwjm","title":"Older releases of better_errors open to Cross-Site Request Forgery attack","description":"### Impact\nbetter_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.\n\n_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)._\n\n### Patches\nStarting with release 2.8.x, CSRF protection is enforced. It is recommended that you upgrade to the latest release, or minimally to \"~\u003e 2.8.3\".\n\n### Workarounds\nThere are no known workarounds to mitigate the risk of using older releases of better_errors.\n\n### References\n- Chris Moberly provided [an example attack that uses a now-patched vulnerability of webpack-dev-server in conjunction with Better Errors](https://about.gitlab.com/blog/2021/09/07/why-are-developers-vulnerable-to-driveby-attacks/)\n\n### For more information\nIf you have any questions or comments about this advisory, please\n- Add to the [discussion in better_errors](https://github.com/BetterErrors/better_errors/discussions/507)\n- Open an issue in [better_errors](https://github.com/BetterErrors/better_errors)\n","status":"published","published":"2021-09-07T23:08:24Z","modified":"2026-07-08T06:29:04.04306914Z","cvss":[{"version":"3.1","score":6.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N","level":"medium"}],"cwes":["CWE-352"],"updated_at":"2026-11-02T15:46:58.04805Z"}]}}