{"id":"CVE-2023-28846","aliases":["GHSA-m875-3xf6-mf78"],"url":"https://o3.security/vulnerability/CVE-2023-28846","summary":"Denial of Service in unpoly-rails","details":"There is a possible Denial of Service (DoS) vulnerability in the unpoly-rails gem that implements the [Unpoly server protocol](https://unpoly.com/up.protocol) for Rails applications.\n\n### Impact\n\nThis issues affects Rails applications that operate as an upstream of a load balancer's that uses [passive health checks](https://docs.nginx.com/nginx/admin-guide/load-balancer/http-health-check/#passive-health-checks).\n\nThe [unpoly-rails](https://github.com/unpoly/unpoly-rails/) gem echoes the request URL as an `X-Up-Location` response header. By making a request with exceedingly long URLs (paths or query string), an attacker can cause unpoly-rails to write a exceedingly large response header.\n\nIf the response header is too large to be parsed by a load balancer downstream of the Rails application, it may cause the load balancer to remove the upstream from a load balancing group. This causes that application instance to become unavailable until a configured timeout is reached or until an active healthcheck succeeds.\n\n\n### Patches\n\nThe fixed release 2.7.2.2+ is available via RubyGems and GitHub.\n\n\n### Workarounds\n\nIf you cannot upgrade to a fixed release, several workarounds are available:\n\n- Configure your load balancer to use active health checks, e.g. by periodically requesting a route with a known response that indicates healthiness.\n- Configure your load balancer so the [maximum size of response headers](https://makandracards.com/operations/537537-nginx-proxy-buffer-tuning) is at least twice the [maximum size of a URL](https://tryhexadecimal.com/guides/http/414-request-uri-too-long).\n- Instead of changing your server configuration you may also configure your Rails application to delete redundant `X-Up-Location` headers set by unpoly-rails:\n  \n  ```ruby\n  class ApplicationController < ActionController::Base\n  \n    after_action :remove_redundant_up_location_header\n    \n    private\n    \n    def remove_redundant_up_location_header\n      if request.original_url == response.headers['X-Up-Location']\n        response.headers.delete('X-Up-Location')\n      end\n    end\n  \n  end\n  ```","published":"2023-03-30T19:57:38.767Z","modified":"2026-08-12T03:51:33.102198491Z","cvss":{"score":5.9,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"unpoly-rails","fixedVersion":"2.7.2.2"}],"fix":{"url":"https://github.com/unpoly/unpoly-rails/commit/cd9ad0007daceeb3b2354fdcab4f88350427bf16","label":"unpoly/unpoly-rails@cd9ad00"},"references":[{"type":"WEB","url":"https://docs.nginx.com/nginx/admin-guide/load-balancer/http-health-check/#passive-health-checks"},{"type":"WEB","url":"https://github.com/unpoly/unpoly-rails/"},{"type":"WEB","url":"https://makandracards.com/operations/537537-nginx-proxy-buffer-tuning"},{"type":"WEB","url":"https://tryhexadecimal.com/guides/http/414-request-uri-too-long"},{"type":"WEB","url":"https://unpoly.com/up.protocol"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/28xxx/CVE-2023-28846.json"},{"type":"ADVISORY","url":"https://github.com/unpoly/unpoly-rails/security/advisories/GHSA-m875-3xf6-mf78"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2023-28846"},{"type":"FIX","url":"https://github.com/unpoly/unpoly-rails/commit/cd9ad0007daceeb3b2354fdcab4f88350427bf16"},{"type":"WEB","url":"https://github.com/rubysec/ruby-advisory-db/blob/master/gems/unpoly-rails/CVE-2023-28846.yml"},{"type":"PACKAGE","url":"https://github.com/unpoly/unpoly-rails"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:33.102198491Z"}}