CVE-2018-1294 in Commons Email
Summary
by MITRE
If a user of Commons-Email (typically an application programmer) passes unvalidated input as the so-called "Bounce Address", and that input contains line-breaks, then the email details (recipients, contents, etc.) might be manipulated. Mitigation: Users should upgrade to Commons-Email 1.5. You can mitigate this vulnerability for older versions of Commons Email by stripping line-breaks from data, that will be passed to Email.setBounceAddress(String).
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Analysis
by VulDB Data Team • 01/15/2020
The vulnerability identified as CVE-2018-1294 represents a critical security flaw within the Apache Commons Email library that exposes applications to email header injection attacks. This vulnerability specifically targets the bounce address parameter handling mechanism within the email sending functionality, creating a pathway for malicious actors to manipulate email headers and potentially execute unauthorized email operations. The issue stems from inadequate input validation in the setBounceAddress method, which fails to properly sanitize user-provided data before incorporating it into email headers.
The technical exploitation of this vulnerability occurs when an attacker supplies a bounce address containing line-break characters such as carriage return and line feed sequences. These control characters allow the attacker to inject additional email headers and manipulate the email structure beyond the intended recipient list and content. When the Commons-Email library processes such input, it concatenates the malicious data directly into the email header without proper sanitization, enabling attackers to append additional recipients, modify message content, or even redirect email delivery entirely. This type of vulnerability falls under the CWE-115 classification for improper input validation and can be categorized as a header injection attack pattern.
The operational impact of this vulnerability extends beyond simple email manipulation to potentially enable more severe security consequences including spam relay abuse, email spoofing, and unauthorized message forwarding. Applications that utilize Commons-Email for sending transactional emails, notifications, or automated communications become vulnerable to exploitation when they accept user input for bounce address configuration without proper validation. Attackers can leverage this vulnerability to send phishing emails, conduct spam campaigns, or disrupt legitimate email services by injecting malicious headers that bypass normal email security controls. The vulnerability particularly affects web applications where user input flows directly into email configuration parameters, creating a direct attack surface for malicious actors.
Organizations using affected versions of Apache Commons-Email should prioritize immediate remediation through upgrading to version 1.5 or later, which includes proper input validation and sanitization for bounce address parameters. For systems unable to upgrade immediately, administrators can implement compensating controls by stripping line-break characters from any data passed to the setBounceAddress method. This mitigation strategy aligns with the principle of least privilege and input sanitization practices recommended in the OWASP Top Ten security framework. The vulnerability demonstrates the critical importance of validating all user-supplied input in security-sensitive contexts and highlights the potential for seemingly benign configuration parameters to become attack vectors when proper sanitization measures are not implemented. Security teams should also consider implementing email header monitoring and anomaly detection systems to identify potential exploitation attempts. This vulnerability serves as a reminder of the importance of following secure coding practices and the potential consequences of inadequate input validation in widely-used library components.