Overview
In the world of cybersecurity, routine software updates and patches are crucial to maintain the security of systems. However, vulnerabilities can sometimes slip through even the most rigorous testing processes. One such vulnerability, CVE-2025-49136, affects the popular standalone, self-hosted newsletter and mailing list manager, listmonk. The vulnerability, if exploited, could lead to a system compromise or data leakage.
This vulnerability has a significant impact on multi-user installations of listmonk, particularly those where non-super-admin users have campaign or template permissions. It is considered critical due to the potential for unauthorized access to sensitive environment variables which could lead to devastating breaches of data and system security.
Vulnerability Summary
CVE ID: CVE-2025-49136
Severity: Critical (CVSS: 9.0)
Attack Vector: Network
Privileges Required: Low
User Interaction: Required
Impact: Unauthorized access to sensitive environment variables leading to potential system compromise or data leakage.
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Product | Affected Versions
listmonk | 4.0.0 – 4.9.9
How the Exploit Works
The exploit takes advantage of the `env` and `expandenv` template functions in listmonk, which are enabled by default. These functions allow the capturing of environment variables on the host system. In single-user installations, this may not be a significant issue. However, in multi-user installations, any non-super-admin user with campaign or template permissions can use the `{{ env }}` template expression to capture sensitive environment variables. This could potentially expose secret keys, passwords, and other confidential information.
Conceptual Example Code
Consider a scenario where a non-super-admin user has campaign permissions in a multi-user listmonk installation. They could potentially exploit this vulnerability as follows:
# Use the `env` template function to capture sensitive environment variables
echo '{{ env "SECRET_KEY" }}' > exploit.tmpl
# Use the template in a campaign
listmonk --campaign exploit.tmplThe above pseudo-code represents an example of how this vulnerability could be exploited, leading to unauthorized access to sensitive environment variables.
Mitigation Guidance
The most effective solution to mitigate this vulnerability is to upgrade listmonk to version 5.0.2 or later. However, if an immediate upgrade is not feasible, implementing a Web Application Firewall (WAF) or Intrusion Detection System (IDS) could serve as temporary mitigation. These measures could help detect and prevent any unauthorized access attempts exploiting this vulnerability.