RackApplication
CVE-2026-32762
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 versions 3.0.0.beta1 to before 3.1.21 and 3.2.0 to before 3.2.6, Rack::Utils.forwarded_values parses the RFC 7239 Forwarded header by splitting on semicolons before handling quoted-string values. Because quoted values may legally contain semicolons, a header can be interpreted by Rack as multiple Forwarded directives rather than as a single quoted for value. In deployments where an upstream proxy, WAF, or intermediary validates or preserves quoted Forwarded values differently, this discrepancy can allow an attacker to smuggle host, proto, for, or by parameters through a single header value. This issue has been patched in versions 3.1.21 and 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 confidenceRack::Utils.forwarded_values incorrectly parses the RFC 7239 Forwarded header by splitting on semicolons before processing quoted-string values. Since quoted values can legally contain semicolons, attackers can craft headers that Rack interprets as multiple Forwarded directives, allowing smuggling of host, proto, for, or by parameters past upstream proxies or WAFs that handle quoted values differently.
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
>= 3.0.0, < 3.1.21>= 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 gem versionRun `gem list rack` or check your Gemfile.lock for the rack gem version entryAffected if The version listed is >= 3.0.0 and < 3.1.21, OR >= 3.2.0 and < 3.2.6
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Confirm Rack is used for header parsingSearch your application code for usage of `Rack::Utils.forwarded_values` or look for middleware that processes the Forwarded HTTP headerAffected if Your application explicitly parses the Forwarded header using Rack::Utils.forwarded_values or similar Rack utilities
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Check if Forwarded header is acceptedReview your Rack middleware stack or proxy configuration to determine if incoming requests may contain a Forwarded header that gets processed by RackAffected if Your application accepts and processes Forwarded headers from upstream clients or proxies without additional validation that predates Rack's parsing
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Test parsing behavior with quoted semicolonsSend a test request with a Forwarded header containing a quoted value with a semicolon, such as `Forwarded: for="[::1];x=y"`, and inspect how Rack::Utils.forwarded_values parses itAffected if The parsed output incorrectly splits the quoted value at the semicolon inside the quotes, producing multiple directives instead of one
You are affected if your Rack gem version falls within the vulnerable ranges AND your application uses Rack to parse Forwarded headers containing quoted values with semicolons.
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 · scoped3.1.213.2.6
Upgrade Rack to version 3.1.21, 3.2.6, or later. If immediate upgrade is not possible, implement validation of Forwarded headers at upstream proxies or WAFs to ensure consistent parsing behavior.
Rack 3.2.6 (or 3.1.21 for the LTS 3.1.x branch)
- Identify the current Rack gem version in your Gemfile or Gemfile.lock
- Run `bundle update rack` to update to the latest version, or specify the fixed version directly with `bundle add rack -v '~> 3.2.6'`
- Run `bundle install` to install the updated gem
- Verify the installed version with `bundle exec rack --version` or by checking Gemfile.lock
- Test your application thoroughly, particularly any functionality that relies on the Forwarded header parsing (e.g., request forwarding, IP whitelisting, proxy detection)
- Deploy to staging and verify that Forwarded header processing works correctly
- Deploy to production
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Rack
Scoped from the published advisory
- Consultation2.0 h
- Implementation1.0 h
- Testing4.0 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 $2,176.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-32762 — 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-2026-32762 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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- Version or environment caveats, and links to real fixes
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