# CVE-2026-125108: Rack: Multipart boundary ambiguity guard in Rack::Multipart::Parser can be bypassed with a quoted boundary value, allowing WAF bypass

Status: published. Published: 2026-11-09. Updated: 2026-11-09.

Rack is a modular Ruby web server interface. Prior to 2.2.25, 3.1.23, and 3.2.8, Rack::Multipart::Parser.parse_boundary can skip a leading empty or quoted boundary parameter in a multipart Content-Type header and accept a later parameter. Rack can therefore parse a request body with a boundary that a conforming intermediary would not derive, allowing form fields or file uploads to reach an application without the intended proxy or web application firewall inspection. This issue is fixed in versions 2.2.25, 3.1.23, and 3.2.8.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- rack / rack: < 2.2.25 (affected); >= 3.0, < 3.1.23 (affected); >= 3.2, < 3.2.8 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 3.7 (low); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-436

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/rack/rack/security/advisories/GHSA-p8x9-v4hv-2w4g (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/rack/rack/commit/19a1a19cb4da97d61c8d5effeb2e927c44370ae9 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/rack/rack/commit/a29512324265790a5536b830490075d0d79323be (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/rack/rack/commit/d5e928b803da30b8e40171dbd4be39bed7daa6fa (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/rack/rack/releases/tag/v2.2.25 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/rack/rack/releases/tag/v3.1.23 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/rack/rack/releases/tag/v3.2.8 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-125108; retrieved 2026-11-09; source updated 2026-11-09

Revision: 32bcffc5b182ef46b1ef3a489176addd01943d45f46f1d7081ab844c448d3362

Canonical: https://y2.dev/cve/CVE-2026-125108

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