# CVE-2026-34831: ruby-rack: Rack is a modular Ruby web server interface

CVE-2026-34831 is fixed in 2 products on 1 platform, first by ruby-rack 3.2.4-1ubuntu1.1, released April 2, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-34831
- Priority: Routine
- CVSS: 6.5 (medium)
- EPSS: 0.0015
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 2, 2026

## Description

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, 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. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | rmt-server opensuse-leap 16.0 | 3.1.0-160000.1.1 | [OPENSUSE-SU-2026:21640-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21640-1.md) | Aug 25, 2026 |
| Linux | rmt-server sles 15.6 | 2.27-150500.3.47.1 | [SUSE-SU-2026:2487-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2487-1.md) | Jun 22, 2026 |
| Linux | rmt-server sles 16.0 | 3.1.0-160000.1.1 | [SUSE-SU-2026:23321-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23321-1.md) | Aug 25, 2026 |
| Linux | ruby-rack Debian 12.15 (bookworm) | 2.2.22-0+deb12u2 | [DEBIAN-CVE-2026-34831](https://patchblox.com/security/data/fix/linux/debian-cve-2026-34831.md) | Apr 2, 2026 |
| Linux | ruby-rack Debian 13.5 (trixie) | 3.1.20-0+deb13u2 | [DEBIAN-CVE-2026-34831](https://patchblox.com/security/data/fix/linux/debian-cve-2026-34831.md) | Apr 2, 2026 |
| Linux | ruby-rack Debian 14 | 3.2.6-2 | [DEBIAN-CVE-2026-34831](https://patchblox.com/security/data/fix/linux/debian-cve-2026-34831.md) | Apr 2, 2026 |
| Linux | ruby-rack Ubuntu 22.04.1 LTS (jammy) | 2.1.4-5ubuntu1.2+esm3 | [ruby-rack 2.1.4-5ubuntu1.2+esm3](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-ruby-rack-2.1.4-5ubuntu1.2-esm3.md) | Apr 30, 2026 |
| Linux | ruby-rack Ubuntu 24.04.5 LTS (noble) | 2.2.7-1ubuntu0.7 | [ruby-rack 2.2.7-1ubuntu0.7](https://patchblox.com/security/data/fix/linux/ubuntu-noble-ruby-rack-2.2.7-1ubuntu0.7.md) | Apr 30, 2026 |
| Linux | ruby-rack Ubuntu 25.10 (questing) | 3.1.16-0.1ubuntu0.3 | [ruby-rack 3.1.16-0.1ubuntu0.3](https://patchblox.com/security/data/fix/linux/ubuntu-questing-ruby-rack-3.1.16-0.1ubuntu0.3.md) | Apr 30, 2026 |
| Linux | ruby-rack Ubuntu 26.04.1 LTS (resolute) | 3.2.4-1ubuntu1.1 | [ruby-rack 3.2.4-1ubuntu1.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-ruby-rack-3.2.4-1ubuntu1.1.md) | Apr 2, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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