CVE-2019-11454: 
Monit vulnerability analysis and mitigation

A persistent cross-site scripting (XSS) vulnerability was discovered in Tildeslash Monit before version 5.25.3. The vulnerability, identified as CVE-2019-11454, was discovered by Zack Flack and disclosed in April 2019. The vulnerability affects the http/cervlet.c component of Monit, a utility for monitoring and managing daemons or similar programs on Unix systems (NVD, Ubuntu Notice).

The vulnerability exists in the http/cervlet.c component where an unsanitized user field of the Authorization header for HTTP Basic Authentication is mishandled during an _viewlog operation. The vulnerability has a CVSS v3.1 Base Score of 6.1 (Medium) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N, indicating network accessibility with low attack complexity and no privileges required (NVD).

The vulnerability allows a remote unauthenticated attacker to introduce arbitrary JavaScript code through manipulation of the Authorization header. When successfully exploited, this could lead to cross-site scripting attacks, potentially compromising the security of the web interface and affecting users who access the _viewlog operation (Debian LTS, Ubuntu Notice).

A proof-of-concept exploit has been publicly released, demonstrating the vulnerability's exploitability. The exploit targets the _viewlog operation and can be triggered by an unauthenticated remote attacker (GitHub Exploit).

The vulnerability was patched in Monit version 5.25.3. Various Linux distributions have released security updates to address this vulnerability: Ubuntu 19.04 (1:5.25.2-3ubuntu0.1), Ubuntu 18.10 (1:5.25.2-1ubuntu0.1), Debian 8 Jessie (1:5.9-1+deb8u2), and Debian 9 Stretch (1:5.20.0-6+deb9u2). Users are strongly recommended to upgrade to the patched versions (Ubuntu Notice, Debian LTS).