CVE-2018-5950

Vulnerability

Mailman versions prior to 2.1.26 contain a reflected cross-site scripting (XSS) vulnerability in the web UI. An attacker can inject arbitrary web script or HTML via a crafted user-options URL [1], [4]. The issue is present in the way the web interface processes parameters without proper sanitization.

Exploitation

The attacker does not require authentication; the vulnerability can be exploited by tricking a user into clicking a specially crafted link to a Mailman user-options page [3]. No special network position is needed beyond the ability to deliver the link (e.g., via email or other channels). The crafted URL includes encoded script that executes in the victim's browser.

Impact

Successful exploitation allows the attacker to execute arbitrary HTML or JavaScript in the context of the victim's browser session. This could lead to session hijacking, defacement, or further attacks against the Mailman instance [4]. Additionally, an information leak was reported where a user-options URL with a VARHELP query fragment bypasses authentication, exposing list membership details [4].

Mitigation

The fix was released in Mailman version 2.1.26 [4]. Red Hat has issued updates for RHEL 7 (mailman-2.1.15-26.el7_4.1) [1]. Ubuntu has provided updated packages (mailman 1:2.1.20-1ubuntu1.2 for 16.04 LTS) [3]. Users should upgrade to the patched version or apply the relevant vendor patch.