CVE-2023-28846: Unpoly is a JavaScript framework for server-side web applications. There is a possible Denial of Service (DoS) vulnerability in the `unpoly-rails` gem...

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.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

1.03%

59.5th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-400

Affected Software

Vendor	Product	Versions
Unpoly	Unpoly-Rails	< 2.7.2.2

References

https://docs.nginx.com/nginx/admin-guide/load-balancer/http-health-check/#passive-health-checksTechnical Description
https://github.com/unpoly/unpoly-rails/Product
https://github.com/unpoly/unpoly-rails/commit/cd9ad0007daceeb3b2354fdcab4f88350427bf16Patch, Vendor Advisory
https://github.com/unpoly/unpoly-rails/security/advisories/GHSA-m875-3xf6-mf78Vendor Advisory
https://makandracards.com/operations/537537-nginx-proxy-buffer-tuningThird Party Advisory
https://tryhexadecimal.com/guides/http/414-request-uri-too-longThird Party Advisory
https://unpoly.com/up.protocolProduct
https://docs.nginx.com/nginx/admin-guide/load-balancer/http-health-check/#passive-health-checksTechnical Description
https://github.com/unpoly/unpoly-rails/Product
https://github.com/unpoly/unpoly-rails/commit/cd9ad0007daceeb3b2354fdcab4f88350427bf16Patch, Vendor Advisory
https://github.com/unpoly/unpoly-rails/security/advisories/GHSA-m875-3xf6-mf78Vendor Advisory
https://makandracards.com/operations/537537-nginx-proxy-buffer-tuningThird Party Advisory
https://tryhexadecimal.com/guides/http/414-request-uri-too-longThird Party Advisory
https://unpoly.com/up.protocolProduct

Timeline

Published: Mar 30, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-28846?

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.

How severe is CVE-2023-28846?

CVE-2023-28846 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 1.03% probability of exploitation in the next 30 days.

How do I fix CVE-2023-28846?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.