GHSA-8vqr-qjwx-82mw
HIGHGHSA-8vqr-qjwx-82mw is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in rack. O3 Security confirms whether GHSA-8vqr-qjwx-82mw is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Rack's multipart parsing without Content-Length header allows unbounded chunked file uploads
Real-World Exposure
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Description
Summary
Rack::Multipart::Parser only wraps the request body in a BoundedIO when CONTENT_LENGTH is present. When a multipart/form-data request is sent without a Content-Length header, such as with HTTP chunked transfer encoding, multipart parsing continues until end-of-stream with no total size limit.
For file parts, the uploaded body is written directly to a temporary file on disk rather than being constrained by the buffered in-memory upload limit. An unauthenticated attacker can therefore stream an arbitrarily large multipart file upload and consume unbounded disk space.
This results in a denial of service condition for Rack applications that accept multipart form data.
Details
Rack::Multipart::Parser.parse applies BoundedIO only when content_length is not nil:
io = BoundedIO.new(io, content_length) if content_length
When CONTENT_LENGTH is absent, the parser reads the multipart body until EOF without a global byte limit.
Although Rack enforces BUFFERED_UPLOAD_BYTESIZE_LIMIT for retained non-file parts, file uploads are handled differently. When a multipart part includes a filename, the body is streamed to a Tempfile, and the retained-size accounting is not applied to that file content. As a result, file parts are not subject to the same upload size bound.
An attacker can exploit this by sending a chunked multipart/form-data request containing a file part and continuously streaming data without declaring a Content-Length. Rack will continue writing the uploaded data to disk until the client stops or the server exhausts available storage.
Impact
Any Rack application that accepts multipart/form-data uploads may be affected if no upstream component enforces a request body size limit.
An unauthenticated attacker can send a large chunked file upload to consume disk space on the application host. This may cause request failures, application instability, or broader service disruption if the host runs out of available storage.
The practical impact depends on deployment architecture. Reverse proxies or application servers that enforce upload limits may reduce or eliminate exploitability, but Rack itself does not impose a total multipart upload limit in this code path when CONTENT_LENGTH is absent.
Mitigation
- Update to a patched version of Rack that enforces a total multipart upload size limit even when
CONTENT_LENGTHis absent. - Enforce request body size limits at the reverse proxy or application server.
- Isolate temporary upload storage and monitor disk consumption for multipart endpoints.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | rack | all versions | 2.2.23 |
| 💎RubyGems | rack | ≥ 3.0.0.beta1&&< 3.1.21 | 3.1.21 |
| 💎RubyGems | rack | ≥ 3.2.0&&< 3.2.6 | 3.2.6 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update rack to 2.2.23 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8vqr-qjwx-82mw is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-8vqr-qjwx-82mw is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-8vqr-qjwx-82mw. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-8vqr-qjwx-82mw in your dependencies?
O3 detects GHSA-8vqr-qjwx-82mw across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.