RackApplication
CVE-2026-26962
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedRack is a modular Ruby web server interface. From version 3.2.0 to before version 3.2.6, Rack::Multipart::Parser unfolds folded multipart part headers incorrectly. When a multipart header contains an obs-fold sequence, Rack preserves the embedded CRLF in parsed parameter values such as filename or name instead of removing the folded line break during unfolding. As a result, applications that later reuse those parsed values in HTTP response headers may be vulnerable to downstream header injection or response splitting. This issue has been patched in version 3.2.6.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThe Rack::Multipart::Parser in versions 3.2.0 through 3.2.5 incorrectly handles obs-fold sequences in multipart headers. When parsing multipart form data, embedded CRLF characters in header values (such as filename or name parameters) are preserved instead of being removed during header unfolding. This allows crafted multipart requests to inject newline characters into parsed values, which can lead to HTTP header injection or response splitting when these values are reused in HTTP response headers.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
RackApplication
>= 3.2.0, < 3.2.6CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed Rack versionRun `gem list rack` or check your Gemfile.lock for the rack gem version, or run `ruby -e "require 'rack'; puts Rack::VERSION"`Affected if The version is 3.2.0, 3.2.1, 3.2.2, 3.2.3, 3.2.4, or 3.2.5 (any version >= 3.2.0 and < 3.2.6)
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Determine if multipart uploads are processedReview your application code for usage of `Rack::Request#params`, `Rack::Multipart`, or any handling of file uploads where `content-disposition` headers with filename or name parameters are parsedAffected if Your application processes multipart form data containing file uploads or form fields with filename or name parameters
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Check if parsed multipart values are used in HTTP response headersSearch your codebase for patterns where parsed multipart parameters (e.g., `params[:filename]`, `params[:name]`, or values from `request.params`) are passed to response headers such as in `redirect`, `headers`, or any method that sets HTTP response headersAffected if Parsed values from multipart requests are directly or indirectly assigned to HTTP response headers without sanitization
You are affected if you have Rack version 3.2.0-3.2.5 AND your application processes multipart form uploads AND any parsed multipart parameter values (filename, name, or other form fields) are used in HTTP response headers.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped3.2.6
Upgrade Rack to version 3.2.6 or later to patch the vulnerable multipart parser. Review application code that uses parsed multipart parameter values in HTTP headers to ensure no downstream header injection exposure remains.
Rack 3.2.6 or later
- Check the current Rack version in your project by running `gem list rack` or inspecting your Gemfile.lock
- Update your Gemfile to specify Rack version 3.2.6 or later: `gem 'rack', '~> 3.2.6'`
- Run `bundle update rack` to apply the security patch
- Verify the installation by checking the installed version with `gem list rack` and restarting your application
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Rack
Scoped from the published advisory
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-26962 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-26962 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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