CVE-2023-28846
Vulnérabilité moyenne dans unpoly-rails (unpoly)
Description
Unpoly is a JavaScript framework for server-side web applications. There is a possible Denial of Service (DoS) vulnerability in the `unpoly-rails` gem that implements the Unpoly server protocol for Rails applications. This issues affects Rails applications that operate as an upstream of a load balancer's that uses passive health checks. The `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. If 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. This issue has been fixed and released as version 2.7.2.2 which is available via RubyGems and GitHub. Users unable to upgrade may: Configure your load balancer to use active health checks, e.g. by periodically requesting a route with a known response that indicates healthiness; Configure your load balancer so the maximum size of response headers is at least twice the maximum size of a URL; or instead of changing your server configuration you may also configure your Rails application to delete redundant `X-Up-Location` headers set by unpoly-rails.
Gravité et risque d'exploitation
CVE-2023-28846 obtient un score CVSS de 5.9/10, soit une gravité moyenne. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 1.03 %, ce qui la place devant 63.3 % des CVE référencées.
Que faire ?
- Vérifiez si unpoly-rails (versions < 2.7.2.2) est présent sur votre parc.
- Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
- À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
- Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.
Références
- https://github.com/unpoly/unpoly-rails/security/advisories/GHSA-m875-3xf6-mf78
- https://github.com/unpoly/unpoly-rails/commit/cd9ad0007daceeb3b2354fdcab4f88350427bf16
- https://docs.nginx.com/nginx/admin-guide/load-balancer/http-health-check/#passive-health-checks
- https://github.com/unpoly/unpoly-rails/
- https://makandracards.com/operations/537537-nginx-proxy-buffer-tuning
- https://tryhexadecimal.com/guides/http/414-request-uri-too-long
- https://unpoly.com/up.protocol