Ruby rack: From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Request parses the Host header
Affects ruby-rackSource GCVE Database
Not known to be exploited · CVSS 6.5 Medium : upgrade to 3.1.16-0.1ubuntu0.3 when convenient.
Data as of 3 Nov 2026, 23:21 UTC
- Patch
- Available – fixed in 3.1.16-0.1ubuntu0.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:NExploitation evidence
Disclosed: evidence found.
CVE published 2 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 3 Nov 2026.
What to do
Upgrade the Ubuntu ruby-rack package to 3.1.16-0.1ubuntu0.3.
Patches and advisories
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.04 LTSruby-rackpkg:deb/ubuntu/ruby-rack?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 25.10ruby-rackpkg:deb/ubuntu/ruby-rack?arch=source&distro=questingOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available and has been released in Rack versions 3.1.21 and 3.2.6. Ubuntu users should update to the fixed package versions (e.g., ruby-rack 3.1.16-0.1ubuntu0.3 or later) as provided in the Ubuntu security notice USN-8182-1. After updating, restart any applications using Rack to apply the fix. No additional mitigation is required if the patch is applied.
Description
A vulnerability in Ruby Rack versions from 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6 allows improper parsing of the Host header. The Rack::Request component uses a regular expression that accepts characters not allowed in RFC-compliant hostnames, which can lead to host header poisoning. This can bypass naive host validation in applications using req.host, req.url, or req.base_url for link generation, redirects, or origin validation. The issue has been fixed in versions 3.1.21 and 3.2.6.