UBUNTU-CVE-2026-26961

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    UBUNTU-CVE-2026-26961

    Published: 2 Apr 2026Last Modified: 4 Nov 2026
    Upstream:
    CVE-2026-26961

    Summary:

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

    References: https://ubuntu.com/security/CVE-2026-26961, https://www.cve.org/CVERecord?id=CVE-2026-26961, https://github.com/rack/rack/security/advisories/GHSA-vgpv-f759-9wx3, https://ubuntu.com/security/notices/USN-8182-1, https://ubuntu.com/security/notices/USN-8989-1

    Affected packages

    Package

    Name: ruby-rack

    Purl: pkg:deb/ubuntu/ruby-rack?arch=source&distro=esm-infra-legacy%2Ftrusty

    Affected ranges

    Type: ECOSYSTEM

    Events:

    Introduced- 0
    Fixed -None

    Affected versions

    1.5.2-1
    1.5.2-1ubuntu0.1~esm1
    1.5.2-3+deb8u3ubuntu1~esm2
    1.5.2-3+deb8u3ubuntu1~esm3
    1.5.2-3+deb8u3ubuntu1~esm4
    1.5.2-3+deb8u3ubuntu1~esm6
    1.5.2-3+deb8u3ubuntu1~esm7
    1.5.2-3+deb8u3ubuntu1~esm8
    1.5.2-3+deb8u3ubuntu1~esm9
    1.5.2-3+deb8u3ubuntu1~esm10
    1.5.2-3+deb8u3ubuntu1~esm11

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High
    UBUNTU-CVE-2026-26961 | CVE-DB