Ruby Rack 3.x < 3.1.21 / 3.2.x < 3.2.6 Multiple Vulnerabilities

medium Nessus Plugin ID 305961

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Synopsis

The remote host has an application installed that is affected by multiple vulnerabilities.

Description

The version of the Rack Ruby library installed on the remote host is 3.0.0.beta1 or later but prior to 3.1.21, or is 3.2.0 or later but prior to 3.2.6. It is, therefore, affected by multiple vulnerabilities:

- Rack::Multipart::Parser#handle_mime_head parses quoted multipart parameters using repeated String#index searches with String#slice! prefix deletion. For escape-heavy quoted values, this causes super-linear processing leading to denial of service (CVE-2026-34827)

- Rack::Request parses Host header using AUTHORITY regex accepting characters not permitted in RFC-compliant hostnames (/, ?, #, @). Applications validating hosts with naive prefix/suffix checks can be bypassed, leading to host header poisoning (CVE-2026-34835)

- Rack::Utils.forwarded_values parses RFC 7239 Forwarded header by splitting on semicolons before handling quoted-string values, allowing parameter smuggling (CVE-2026-32762)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Solution

Upgrade to Rack version 3.1.21 or 3.2.6 or later.

Plugin Details

Severity: Medium

ID: 305961

File Name: ruby_gem_rack_3_2_6_2026.nasl

Version: 1.3

Type: Local

Agent: windows, macosx, unix

Family: Misc.

Published: 4/10/2026

Updated: 4/13/2026

Configuration: Enable thorough checks (optional)

Supported Sensors: Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.4

CVSS v2

Risk Factor: High

Base Score: 8.5

Temporal Score: 6.7

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:P/A:C

CVSS Score Source: CVE-2026-34827

CVSS v3

Risk Factor: Medium

Base Score: 6.5

Temporal Score: 5.9

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

CVSS Score Source: CVE-2026-34835

Vulnerability Information

CPE: cpe:/a:ruby:rack

Required KB Items: Host/ruby/modules/enumerated

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 4/2/2026

Vulnerability Publication Date: 4/2/2026

Reference Information

CVE: CVE-2026-32762, CVE-2026-34827, CVE-2026-34835

IAVB: 2026-B-0085

Detections

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