RackApplication
CVE-2026-34830
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. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Sendfile#map_accel_path interpolates the value of the X-Accel-Mapping request header directly into a regular expression when rewriting file paths for X-Accel-Redirect. Because the header value is not escaped, an attacker who can supply X-Accel-Mapping to the backend can inject regex metacharacters and control the generated X-Accel-Redirect response header. In deployments using Rack::Sendfile with x-accel-redirect, this can allow an attacker to cause nginx to serve unintended files from configured internal locations. This issue has been patched in versions 2.2.23, 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::Sendfile#map_accel_path interpolates the X-Accel-Mapping request header directly into a regular expression without escaping, allowing attackers to inject regex metacharacters and manipulate the X-Accel-Redirect response header. This enables attackers to cause nginx to serve unintended files from configured internal locations.
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
< 2.2.23>= 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
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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 versionAffected if Version is < 2.2.23, or >= 3.0.0 and < 3.1.21, or >= 3.2.0 and < 3.2.6
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Verify Rack::Sendfile middleware is loadedSearch your application code for `use Rack::Sendfile` in config.ru, config/application.rb, or relevant middleware configuration filesAffected if Rack::Sendfile middleware is present in the middleware stack
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Confirm X-Accel-Mapping header processing is activeCheck if your application forwards or processes the X-Accel-Mapping request header; inspect request handling code for header access patterns like `env['HTTP_X_ACCEL_MAPPING']`Affected if The application processes X-Accel-Mapping headers from incoming requests
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Check for X-Accel-Redirect usage in responsesSearch your codebase for places where `X-Accel-Redirect` header is set, or where `map_accel_path` method from Rack::Sendfile is calledAffected if Your application uses X-Accel-Redirect to delegate file serving to nginx
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Review nginx configuration for internal locationsInspect nginx.conf or included configuration files for `internal` directives that define locations accessible via X-Accel-Redirect (typically under /x-accel-redirect-path)Affected if Nginx has internal locations configured that could be manipulated through the vulnerable header
You are affected if your Rack version falls within the vulnerable ranges AND your application uses Rack::Sendfile with X-Accel-Mapping header processing.
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 · scoped2.2.233.1.213.2.6
Upgrade to Rack versions 2.2.23, 3.1.21, or 3.2.6 which contain the patch, or implement input validation to escape regex metacharacters in the X-Accel-Mapping header before use.
Rack 2.2.23, 3.1.21, or 3.2.6 (depending on your major version branch)
- Identify the current Rack version in your Gemfile or Gemfile.lock
- Run `bundle update rack` or specify the appropriate version in your Gemfile
- Verify the installed version matches one of the fixed releases: 2.2.23, 3.1.21, or 3.2.6
- Run your test suite to confirm the upgrade does not break your application
- Deploy the updated application
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Rack
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 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 $2,800.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-34830 — 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-2026-34830 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
- No weaponised exploit code, or anything meant to cause harm
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