Rack::Session is a session management implementation for Rack. From 2.0.0 to before 2.1.2, Rack::Session::Cookie incorrectly handles decryption failures when configured with secrets:. If cookie decryption fails, the implementation falls back to a default decoder instead of rejecting the cookie. This allows an unauthenticated attacker to supply a crafted session cookie that is accepted as valid session data without knowledge of any configured secret. Because this mechanism is used to load session state, an attacker can manipulate session contents and potentially gain unauthorized access. This vulnerability is fixed in 2.1.2.

The remote Debian 13 host has a package installed that is affected by a vulnerability as referenced in the dsa-6542 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6542-1                   security@debian.org     https://www.debian.org/security/                       Moritz Muehlenhoff     October 04, 2026                      https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : ruby-rack-session     CVE ID         : CVE-2026-39324

    It was discovered that incorrect error handling in ruby-rack-session     may result in authentication bypass or privilege escalation in some     setups.

    For the stable distribution (trixie), this problem has been fixed in     version 2.1.1-0.1+deb13u1.

    We recommend that you upgrade your ruby-rack-session packages.

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

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

    Mailing list: debian-security-announce@lists.debian.org

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

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

The remote Ubuntu 25.10 host has a package installed that is affected by a vulnerability as referenced in the USN-8190-1 advisory.

    SeungMyung Lee discovered that Rack::Session did not properly reject cookies upon decryption failure. A     remote attacker could use this issue to manipulate session contents and possibly gain unauthorized access.

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

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

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - Rack::Session is a session management implementation for Rack. From 2.0.0 to before 2.1.2,
    Rack::Session::Cookie incorrectly handles decryption failures when configured with secrets:. If cookie
    decryption fails, the implementation falls back to a default decoder instead of rejecting the cookie. This
    allows an unauthenticated attacker to supply a crafted session cookie that is accepted as valid session
    data without knowledge of any configured secret. Because this mechanism is used to load session state, an
    attacker can manipulate session contents and potentially gain unauthorized access. This vulnerability is
    fixed in 2.1.2. (CVE-2026-39324)

ID	Name	Product	Family	Type	Severity
362912	Debian dsa-6542 : ruby-rack-session - security update	Nessus	Debian Local Security Checks	Local	critical
307893	Ubuntu 25.10 : Rack::Session vulnerability (USN-8190-1)	Nessus	Ubuntu Local Security Checks	Local	critical
440003	SCA: security update for rack-session (GHSA-33qg-7wpp-89cq)	Tenable Cloud Security	SCA Checks	Local	critical
440003	SCA: security update for rack-session (GHSA-33qg-7wpp-89cq)	Tenable Self-Hosted Container Security	SCA Checks	Local	critical

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CVE-2026-39324

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