Rack: Forwarded Header semicolon injection enables Host and Scheme spoofing

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.8 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-32762: 0.19% estimated exploitation activity in the next 30 days; percentile 8.22 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Rack::Utils.forwardedvalues parses the RFC 7239 Forwarded header by splitting on semicolons before handling quoted-string values. Because quoted values may legally contain semicolons, a header such as: can be interpreted by Rack as multiple Forwarded directives rather than as a single quoted for value. In deployments where an upstream proxy, WAF, or intermediary validates or preserves quoted Forwarded values differently, this discrepancy can allow an attacker to smuggle host, proto, for, or by parameters through a single header value. Details Rack::Utils.forwardedvalues processes the header using logic equivalent to: The method splits on ; before it parses individual name=value pairs. This is inconsistent with RFC 7239, which permits quoted-string values, and quoted strings may contain semicolons as literal content. As a result, a header value such as: is not treated as a single for value. Instead, Rack may interpret it as if the client had supplied separate for, host, and…

Published by the source

2 Apr 2026, 20:31 UTC

Last modified by the source

13 May 2026, 16:17 UTC

Source last checked

26 Oct 2026, 15:52 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-qfgr-crr9-7r49

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-32762

Advisory: Rack: Forwarded Header semicolon injection enables Host and Scheme spoofing
IDs: CVE-2026-32762, GHSA-qfgr-crr9-7r49
Record: https://patchnext.com/advisories/cve-2026-32762 (revision 1, source checked 26 Oct 2026, 15:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: rack 3.2.6, 3.1.21. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems rack: affected >= 3.0.0.beta1, < 3.1.21; >= 3.2.0, < 3.2.6; fixed in 3.1.21, 3.2.6

## Suggested inspection (read-only)
- RubyGems rack: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on rack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-qfgr-crr9-7r49 (GitHub-reviewed advisory GHSA-qfgr-crr9-7r49 lists affected ranges: RubyGems rack >=3.0.0.beta1 =3.2.0 <3.2.6)

Commands are suggestions: review each one before running it.