CVE-2026-32762: Rack interpretation conflict in Forwarded header parsing

CVE-2026-32762 · Severity: medium · CVSS 4.8 · Published 2026-04-02

Rack is a standard interface used by Ruby web applications to communicate with web servers. A flaw in how it handles network headers allows attackers to manipulate information about the original request, such as the website's address or security protocol. This can lead to security issues like unauthorized redirects, incorrect logging, or the generation of malicious password reset links.

Technologies: rack (RubyGems). Vendors: RubyGems.

Quick answers

Is CVE-2026-32762 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-32762 being exploited in the wild.
How severe is CVE-2026-32762?
Medium severity, with a CVSS score of 4.8, published 2 April 2026.
Which products and versions are affected?
rack (RubyGems) ECOSYSTEM:introduced=3.0.0.beta1,fixed=3.1.21.
Is there a fix for CVE-2026-32762?
Yes. rack (RubyGems): upgrade to 3.1.21 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-32762 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-32762?
Check whether you run rack (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • rack (RubyGems): upgrade to 3.1.21 or later
    bundle update rack

Technical details

The vulnerability exists in Rack::Utils.forwarded_values, which incorrectly parses RFC 7239 Forwarded headers by splitting on semicolons before processing quoted-string values. Because semicolons are legally permitted within quoted strings, an attacker can craft a header that Rack interprets as multiple directives (e.g., host, proto) while an upstream proxy or WAF sees it as a single value. This interpretation conflict allows for header smuggling. Attackers can exploit this to spoof request metadata such as req.host and req.scheme, which may impact security-sensitive operations like absolute URL generation or IP-based access control. The issue is patched in versions 3.1.21 and 3.2.6.

Affected products

  • Rack Rack >= 3.0.0.beta1, < 3.1.21; >= 3.2.0, < 3.2.6

Identifiers

  • CVE-2026-32762
  • GHSA-qfgr-crr9-7r49

Timeline

  • 2026-04-01: advisory: GitHub advisory GHSA-qfgr-crr9-7r49 published
  • 2026-04-02: disclosed: CVE-2026-32762 published

References

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