Debian dla-4706 : ruby-rack - security update

high Nessus Plugin ID 331301

Synopsis

The remote Debian host is missing one or more security-related updates.

Description

The remote Debian 11 / 12 host has a package installed that is affected by multiple vulnerabilities as referenced in the dla-4706 advisory.

- ------------------------------------------------------------------------- Debian LTS Advisory DLA-4706-1 [email protected] https://www.debian.org/lts/security/ Abhijith PA July 31, 2026 https://wiki.debian.org/LTS
- -------------------------------------------------------------------------

Package : ruby-rack Version : 2.1.4-3+deb11u6 2.2.22-0+deb12u2 CVE ID : CVE-2026-26961 CVE-2026-34230 CVE-2026-34763 CVE-2026-34785 CVE-2026-34786 CVE-2026-34826 CVE-2026-34829 CVE-2026-34830 CVE-2026-34831

Multiple vulnerabilities were found in ruby-rack, a modular Ruby webserver interface

CVE-2026-26961

Rack::Multipart::Parser extracts the boundary parameter from multipart/form-data using a greedy regular expression. When a Content-Type header contains multiple boundary parameters, Rack selects the last one rather than the first. In deployments where an upstream proxy, WAF, or intermediary interprets the first boundary parameter, this mismatch can allow an attacker to smuggle multipart content past upstream inspection and have Rack parse a different body structure than the intermediary validated.

CVE-2026-34230

Rack::Utils.select_best_encoding processes Accept-Encoding values with quadratic time complexity when the header contains many wildcard (*) entries. Because this method is used by Rack::Deflater to choose a response encoding, an unauthenticated attacker can send a single request with a crafted Accept-Encoding header and cause disproportionate CPU consumption on the compression middleware path. This results in a denial of service condition for applications using Rack::Deflater.

CVE-2026-34763

Rack::Directory interpolates the configured root path directly into a regular expression when deriving the displayed directory path. If root contains regex metacharacters such as +, *, or ., the prefix stripping can fail and the generated directory listing may expose the full filesystem path in the HTML output.

CVE-2026-34785

Rack::Static determines whether a request should be served as a static file using a simple string prefix check. When configured with URL prefixes such as /css, it matches any request path that begins with that string, including unrelated paths such as /css-config.env or /css-backup.sql. As a result, files under the static root whose names merely share the configured prefix may be served unintentionally, leading to information disclosure.

CVE-2026-34786

Rack::Static#applicable_rules evaluates several header_rules types against the raw URL-encoded PATH_INFO, while the underlying file-serving path is decoded before the file is served. As a result, a request for a URL-encoded variant of a static path can serve the same file without the headers that header_rules were intended to apply. In deployments that rely on Rack::Static to attach security-relevant response headers to static content, this can allow an attacker to bypass those headers by requesting an encoded form of the path.

CVE-2026-34826

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.

CVE-2026-34829

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.

CVE-2026-34830

Rack::Sendfile#map_accel_path interpolates the value of the X-Accel-Mapping request header directly into a regular expression when rewriting file paths for X-Accel-Redirect. Because the header value is not escaped, an attacker who can supply X-Accel-Mapping to the backend can inject regex metacharacters and control the generated X-Accel-Redirect response header. In deployments using Rack::Sendfile with x-accel-redirect, this can allow an attacker to cause nginx to serve unintended files from configured internal locations.

CVE-2026-34831

Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value.

For Debian 11 bullseye, these problems have been fixed in version 2.1.4-3+deb11u6.

For Debian 12 bookworm, these problems have been fixed in version 2.2.22-0+deb12u2.

We recommend that you upgrade your ruby-rack packages.

For the detailed security status of ruby-rack please refer to its security tracker page at:
https://security-tracker.debian.org/tracker/ruby-rack

Further information about Debian LTS security advisories, how to apply these updates to your system and frequently asked questions can be found at: https://wiki.debian.org/LTS

Tenable has extracted the preceding description block directly from the Debian security advisory.

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

Solution

Upgrade the ruby-rack packages.

Plugin Details

Severity: High

ID: 331301

File Name: debian_DLA-4706.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Debian Local Security Checks

Published: 7/30/2026

Updated: 7/30/2026

Supported Sensors: Agentless Assessment, Continuous Assessment, Frictionless Assessment Agent, Nessus Agent, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.73

CVSS v2

Risk Factor: High

Base Score: 7.8

Temporal Score: 6.1

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

CVSS Score Source: CVE-2026-34830

CVSS v3

Risk Factor: High

Base Score: 7.5

Temporal Score: 6.7

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

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

Vulnerability Information

CPE: cpe:/o:debian:debian_linux:11.0, cpe:/o:debian:debian_linux:12.0, p-cpe:/a:debian:debian_linux:ruby-rack

Required KB Items: Host/local_checks_enabled, Host/Debian/release, Host/Debian/dpkg-l

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 7/31/2026

Vulnerability Publication Date: 2/28/2024

Reference Information

CVE: CVE-2024-26141, CVE-2026-26961, CVE-2026-34230, CVE-2026-34763, CVE-2026-34785, CVE-2026-34786, CVE-2026-34826, CVE-2026-34829, CVE-2026-34830, CVE-2026-34831

Detections

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