ESB-2026.3876

=========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2026.3876 USN-8182-1: Rack vulnerabilities 17 April 2026 =========================================================================== AUSCERT Security Bulletin Summary --------------------------------- Product: Rack Publisher: Ubuntu Operating System: Ubuntu Resolution: Patch/Upgrade CVE Names: CVE-2026-26962 CVE-2026-32762 CVE-2026-34230 CVE-2026-34763 CVE-2026-34785 CVE-2026-34786 CVE-2026-34826 CVE-2026-34827 CVE-2026-34829 CVE-2026-34830 CVE-2026-34831 CVE-2026-34835 CVE-2026-26961 Original Bulletin: https://ubuntu.com/security/notices/USN-8182-1 Comment: CVSS (Max): 7.5 CVE-2026-34829 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) CVSS Source: Ubuntu Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H EPSS (Max): 0.1% (28th) CVE-2026-34835 2026-04-16 - --------------------------BEGIN INCLUDED TEXT-------------------- USN-8182-1: Rack vulnerabilities Publication date 17 April 2026 Overview Several security issues were fixed in Rack. Releases 25.10 24.04 LTS 22.04 LTS 20.04 LTS 18.04 LTS 16.04 LTS 14.04 LTS --------------------------------------------------------------------------------- Open side navigation Packages o ruby-rack - modular Ruby webserver interface Details Andrew Lacambra discovered that Rack did not properly parse certain regular expressions. An attacker could possibly use this issue to bypass network security filters. This issue only affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. ( CVE-2026-26961 ) William T. Nelson discovered that Rack did not handle multipart headers correctly. An attacker could possibly use this issue to cause downstream parsing issues or a denial of service. This issue only affected Ubuntu 25.10. ( CVE-2026-26962 ) It was discovered that Rack did not handle the Forwarded header correctly. An attacker could possibly use this issue to manipulate header values. This issue only affected Ubuntu 25.10. ( CVE-2026-32762 ) It was discovered that Rack could consume excessive CPU when handling certain Accept-Encoding values. An attacker could possibly use this issue to cause a denial of service. ( CVE-2026-34230 ) Haruki Oyama discovered that certain configurations of Rack could erroneously fail to derive the displayed directory path, and expose the full filesystem path. An attacker could possibly use this issue to disclose deployment details such as layout and usernames. ( CVE-2026-34763 ) It was discovered that Rack did not properly handle static file paths. An attacker could possibly use this issue to exfiltrate unintentionally served data. ( CVE-2026-34785 ) Haruki Oyama discovered that Rack did not apply header rules to certain requests for URL-encoded static paths. An attacker could possibly use this issue to bypass security-relevant response headers. This issue only affected Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. ( CVE-2026-34786 ) It was discovered that Rack did not limit the number of ranges requested in the Range header. An attacker could possibly use this issue to cause a denial of service. This issue only affected Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. ( CVE-2026-34826 ) It was discovered that Rack could consume excessive CPU when parsing certain multipart parameters. An attacker could possibly use this to cause a denial of service. This issue only affected Ubuntu 25.10. ( CVE-2026-34827 ) It was discovered that Rack could consume unbounded disk space when handling requests without a Content-Length header. An attacker could possibly use this issue to cause a denial of service. This issue only affected Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. ( CVE-2026-34829 ) Mehtab Zafar discovered that Rack directly interpreted the X-Accel-Mapping header as a regular expression without escaping. An attacker could possibly use this issue to exfiltrate arbitrary files from internal locations. This issue only affected Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. ( CVE-2026-34830 ) It was discovered that Rack did not properly handle messages with Unicode. An attacker could possibly use this issue to cause a denial of service. This issue only affected Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 25.10. ( CVE-2026-34831 ) It was discovered that Rack did not properly parse the Host header. An attacker could possibly use this issue to bypass security filters or poison generated links. This issue only affected Ubuntu 25.10. ( CVE-2026-34835 ) --------------------------------------------------------------------------------- Update instructions The problem can be corrected by updating your system to the following package versions: Ubuntu Package Version Release 25.10 ruby-rack - 3.1.16-0.1ubuntu0.3 questing 24.04 LTS ruby-rack - 2.2.7-1ubuntu0.7 noble 22.04 ruby-rack - 2.1.4-5ubuntu1.2+esm3 Ubuntu Pro Fix available with Ubuntu LTS Pro via ESM Apps. A community fix might become publicly available in jammy the future. 20.04 ruby-rack - 2.0.7-2ubuntu0.1+esm10 Ubuntu Pro Fix available with LTS Ubuntu Pro via ESM Apps. A community fix might become publicly focal available in the future. 18.04 ruby-rack - 1.6.4-4ubuntu0.2+esm10 Ubuntu Pro Fix available with LTS Ubuntu Pro via ESM Apps. A community fix might become publicly bionic available in the future. 16.04 ruby-rack - 1.6.4-3ubuntu0.2+esm10 Ubuntu Pro Fix available with LTS Ubuntu Pro via ESM Apps. A community fix might become publicly xenial available in the future. librack-ruby - 1.5.2-3+deb8u3ubuntu1~esm11 Ubuntu Pro Fix available with Ubuntu Pro via Legacy Support add-on. 14.04 librack-ruby1.8 - 1.5.2-3+deb8u3ubuntu1~esm11 Ubuntu Pro Fix available LTS with Ubuntu Pro via Legacy Support add-on. trusty librack-ruby1.9.1 - 1.5.2-3+deb8u3ubuntu1~esm11 Ubuntu Pro Fix available with Ubuntu Pro via Legacy Support add-on. ruby-rack - 1.5.2-3+deb8u3ubuntu1~esm11 Ubuntu Pro Fix available with Ubuntu Pro via Legacy Support add-on. --------------------------------------------------------------------------------- References o CVE-2026-34835 o CVE-2026-34831 o CVE-2026-34830 o CVE-2026-34829 o CVE-2026-34827 o CVE-2026-34826 o CVE-2026-34786 o CVE-2026-34785 o CVE-2026-34763 o CVE-2026-34230 o CVE-2026-32762 o CVE-2026-26962 o CVE-2026-26961 --------------------------------------------------------------------------------- - --------------------------END INCLUDED TEXT---------------------- You have received this e-mail bulletin as a result of your organisation's registration with AUSCERT. 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