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Fencer Vulns
medium 6.1

CVE-2021-22903 json

Possible Open Redirect Vulnerability in Action Pack

published 2021-05-05 5 y ago modified 2026-06-17 4 mo ago also GHSA-5hq2-xf89-9jxq , EUVD-2021-0957

cvss
6.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 69%
public exploits
0
none known

Summary

The actionpack ruby gem before 6.1.3.2 suffers from a possible open redirect vulnerability. Specially crafted 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. This is similar to CVE-2021-22881. Strings in config.hosts that do not have a leading dot are converted to regular expressions without proper escaping. This causes, for example, `config.hosts << "sub.example.com"` to permit a request with a Host header value of `sub-example.com`.

Patch / fix

  • rubygems actionpack 6.1.3.2
  • rubyonrails rails 6.1.3.2

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-22903 updated cvss 6.5

rubygem-actionpack: Possible Open Redirect Vulnerability in Action Pack

  • Red Hat CloudForms Management Engine 5 cfme-gemset, cfme-amazon-smartstate Red Hat Satellite 6 tfm-rubygem-actionpack, tfm-ror52-rubygem-actionpack
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.23% chance of exploitation in the next 30 days, higher than 69% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 2.0 5.8 AV:N/AC:M/Au:N/C:P/I:P/A:N
GitHub 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
rubygems actionpack
>=6.1.0.rc2, <6.1.3.2
6.1.3.2

Affected products

  • n/a https://github.com/rails/rails

Classification

Weakness
  • CWE-601 URL Redirection to Untrusted Site
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.