CVE-2026-34826 — Rack: Unbounded Range Count in get_byte_ranges Enables DoS

Affected: rack

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Utils.get_byte_ranges parses the HTTP Range header without limiting the number of individual byte ranges. Although the existing fix for CVE-2024-26141 rejects ranges whose total byte coverage exceeds the file size, it does not restrict the count of ranges. An attacker can supply many small overlapping ranges such as 0-0,0-0,0-0,... to trigger disproportionate CPU, memory, I/O, and bandwidth consumption per request. This results in a denial of service condition in Rack file-serving paths that process multipart byte range responses. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

GHSA-x8cg-fq8g-mxfx — Rack's multipart byte range processing allows denial of service via excessive overlapping ranges

Affected: RubyGems: rack

## Summary

`Rack::Utils.get_byte_ranges` parses the HTTP `Range` header without limiting the number of individual byte ranges. Although the existing fix for CVE-2024-26141 rejects ranges whose total byte coverage exceeds the file size, it does not restrict the count of ranges. An attacker can supply many small overlapping ranges such as `0-0,0-0,0-0,...` to trigger disproportionate CPU, memory, I/O, and bandwidth consumption per request.

This results in a denial of service condition in Rack file-serving paths that process multipart byte range responses.

## Details

`Rack::Utils.get_byte_ranges` accepts a comma-separated list of byte ranges and validates them based on their aggregate size, but does not impose a limit on how many individual ranges may be supplied.

As a result, a request such as:

```http Range: bytes=0-0,0-0,0-0,0-0,... ```

can contain thousands of overlapping one-byte ranges while still satisfying the total-size check added for CVE-2024-26141.

When such a header is processed by Rack’s file-serving code, each range causes additional work, including multipart response generation, per-range iteration, file seek and read operations, and temporary string allocation for response size calculation and output. This allows a relatively small request header to trigger disproportionately expensive processing and a much larger multipart response.

The issue is distinct from CVE-2024-26141. That fix prevents range sets whose total byte coverage exceeds the file size,…

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CVE-2026-34826 — Rack: Unbounded Range Count in get_byte_ranges Enables DoS

GHSA-x8cg-fq8g-mxfx — Rack's multipart byte range processing allows denial of service via excessive overlapping ranges