CVE-2026-26962: Rack CRLF injection in Rack::Multipart::Parser

CVE-2026-26962 · Severity: medium · CVSS 4.8 · Published 2026-04-02

Rack is a foundational software library used by many Ruby web applications to handle web requests. A flaw in how it processes file uploads allows attackers to submit specially formatted filenames that contain hidden line-break characters. If an application later uses these filenames in its own web responses, it could lead to security issues like session hijacking or the delivery of malicious content to other users.

Technologies: rack (RubyGems). Vendors: RubyGems.

Quick answers

Is CVE-2026-26962 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-26962 being exploited in the wild.
How severe is CVE-2026-26962?
Medium severity, with a CVSS score of 4.8, published 2 April 2026.
Which products and versions are affected?
rack (RubyGems) >= 3.2.0, < 3.2.6, ECOSYSTEM:introduced=3.2.0,fixed=3.2.6.
Is there a fix for CVE-2026-26962?
Yes. rack (RubyGems): upgrade to 3.2.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-26962 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-26962?
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 3.2.6 or later
    bundle update rack

Technical details

A CRLF injection vulnerability exists in Rack::Multipart::Parser due to improper unfolding of 'obs-fold' sequences in multipart headers. When parsing multipart form data, the library fails to remove embedded carriage return and line feed (CRLF) characters from header parameters such as 'filename' or 'name'. An attacker can exploit this by submitting a multipart request with folded headers containing these sequences. If the resulting parsed values are subsequently used by the application to construct HTTP response headers without further sanitization, it can result in HTTP response splitting or header injection. This issue is patched in version 3.2.6.

Affected products

  • Rack Rack >= 3.2.0, < 3.2.6

Identifiers

  • CVE-2026-26962
  • GHSA-rx22-g9mx-qrhv

Timeline

  • 2026-04-01: advisory: GitHub advisory published by maintainers
  • 2026-04-02: disclosed: CVE published to NVD
  • 2026-04-02: patched: Version 3.2.6 released to address the issue

References

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