CVE-2026-34829

Summary

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, 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. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Affected Software

VendorProductVersion RangeStatus
rackrack< 2.2.23affected
rackrack>= 3.0.0.beta1, < 3.1.21affected
rackrack>= 3.2.0, < 3.2.6affected

Weaknesses

  • CWE-400: CWE-400: Uncontrolled Resource Consumption
  • CWE-770: CWE-770: Allocation of Resources Without Limits or Throttling

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: yes
    • Technical Impact: partial

rack: Rack: Denial of Service via unbounded multipart file upload

Additional References

References