CVE-2023-28846

CVE-2023-28846 is a medium-severity vulnerability in Unpoly Unpoly-rails with a CVSS 3.x base score of 5.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-400.

Key facts

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.

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 3.x base score of 5.9, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2023-28846 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (60th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-28846?
CVE-2023-28846 affects Unpoly Unpoly-rails. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2023-28846?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2023-28846 published?
CVE-2023-28846 was published on 2023-03-30 and last updated on 2026-06-17.

References

Affected products (1)

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