CVE-2020-2252 in Mailer Plugin
Summary
by MITRE
Jenkins Mailer Plugin 1.32 and earlier does not perform hostname validation when connecting to the configured SMTP server.
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Analysis
by VulDB Data Team • 09/16/2020
The Jenkins Mailer Plugin vulnerability CVE-2020-2252 represents a critical security flaw in the email notification functionality of the Jenkins continuous integration platform. This vulnerability affects versions 1.32 and earlier of the Mailer Plugin, which is widely used by organizations to send email notifications for build results, system alerts, and other automated communications. The issue stems from insufficient hostname validation during SMTP server connections, creating potential attack vectors that could compromise the integrity and confidentiality of email communications within Jenkins environments.
The technical flaw in CVE-2020-2252 manifests as a lack of proper hostname verification when establishing connections to SMTP servers configured within Jenkins. This omission allows attackers to potentially redirect email traffic to malicious servers through various attack vectors including DNS hijacking, man-in-the-middle attacks, or compromised DNS servers. The vulnerability specifically falls under CWE-295 which addresses improper certificate validation or hostname verification in network communications. When Jenkins attempts to send email notifications, it connects to the configured SMTP server without validating that the server's hostname matches the expected certificate, creating a window for attackers to intercept or manipulate email communications.
The operational impact of this vulnerability extends beyond simple email delivery failures, potentially enabling sophisticated attack scenarios that could compromise entire Jenkins infrastructures. Attackers could exploit this weakness to intercept sensitive build notifications, system alerts, and other communications that might contain confidential information such as build artifacts, deployment details, or security event notifications. The vulnerability also opens possibilities for spamming activities where malicious actors could use compromised Jenkins instances to send large volumes of unsolicited emails through the configured SMTP servers. From an ATT&CK framework perspective, this vulnerability maps to T1190 - Exploit Public-Facing Application and T1071.004 - Application Layer Protocol: DNS, as it allows attackers to manipulate DNS resolution to redirect SMTP traffic to malicious endpoints.
Organizations utilizing affected Jenkins Mailer Plugin versions face significant risks including data leakage through intercepted email communications, potential credential exposure in build notifications, and increased attack surface for broader network compromise. The vulnerability is particularly concerning in enterprise environments where Jenkins is used for critical CI/CD processes and where email notifications contain sensitive operational information. Security teams must consider the potential for this vulnerability to be exploited as part of larger attack chains where compromised Jenkins instances serve as entry points for further lateral movement within networks. The lack of hostname validation creates persistent security gaps that remain exploitable until proper patching occurs, making this vulnerability particularly dangerous in environments with limited network segmentation or monitoring capabilities.
Mitigation strategies for CVE-2020-2252 primarily involve immediate patching of the Mailer Plugin to versions 1.33 or later where hostname validation has been implemented. Organizations should also consider implementing network-level controls such as DNS filtering, SMTP traffic monitoring, and certificate pinning for critical Jenkins configurations. Additional defensive measures include regular security audits of Jenkins configurations, implementation of network segmentation to isolate Jenkins instances from critical systems, and enhanced monitoring of email delivery patterns for signs of potential interception or redirection. The vulnerability serves as a reminder of the critical importance of proper hostname validation in network communications and demonstrates how seemingly minor configuration flaws can create significant security risks in automated systems.