EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
actionpack💎actionpackReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Overview
There is a possible open redirect vulnerability in the Host Authorization middleware in Action Pack. This vulnerability has been assigned the CVE identifier CVE-2021-22942.
Versions Affected: >= 6.0.0. Not affected: < 6.0.0 Fixed Versions: 6.1.4.1, 6.0.4.1
Impact
Specially crafted “X-Forwarded-Host” headers in combination with certain “allowed host” formats can cause the Host Authorization middleware in Action Pack to redirect users to a malicious website.
Impacted applications will have allowed hosts with a leading dot. For example, configuration files that look like this:
config.hosts << '.EXAMPLE.com'
When an allowed host contains a leading dot, a specially crafted Host header can be used to redirect to a malicious website.
This vulnerability is similar to CVE-2021-22881, but CVE-2021-22881 did not take in to account domain name case sensitivity.
Releases
The fixed releases are available at the normal locations.
Workarounds
In the case a patch can’t be applied, the following monkey patch can be used in an initializer:
module ActionDispatch
class HostAuthorization
HOSTNAME = /[a-z0-9.-]+|\[[a-f0-9]*:[a-f0-9.:]+\]/i
VALID_ORIGIN_HOST = /\A(#{HOSTNAME})(?::\d+)?\z/
VALID_FORWARDED_HOST = /(?:\A|,[ ]?)(#{HOSTNAME})(?::\d+)?\z/
private
def authorized?(request)
origin_host =
request.get_header("HTTP_HOST")&.slice(VALID_ORIGIN_HOST, 1) || ""
forwarded_host =
request.x_forwarded_host&.slice(VALID_FORWARDED_HOST, 1) || ""
@permissions.allows?(origin_host) &&
(forwarded_host.blank? || @permissions.allows?(forwarded_host))
end
end
end
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | actionpack | ≥ 6.0.0&&< 6.0.4.1 | 6.0.4.1 |
| 💎RubyGems | actionpack | ≥ 6.1.0&&< 6.1.4.1 | 6.1.4.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for actionpack. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update actionpack to 6.0.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-2rqw-v265-jf8c is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-2rqw-v265-jf8c is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-2rqw-v265-jf8c. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-2rqw-v265-jf8c in your dependencies?
O3 detects GHSA-2rqw-v265-jf8c across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.