CVE-2020-28247 in lettre library
Summary
by MITRE • 11/12/2020
The lettre library through 0.10.0-alpha for Rust allows arbitrary sendmail option injection via transport/sendmail/mod.rs.
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Analysis
by VulDB Data Team • 12/06/2020
The CVE-2020-28247 vulnerability represents a critical security flaw in the lettre library version 0.10.0-alpha and earlier, specifically within the sendmail transport implementation. This vulnerability arises from insufficient input validation and sanitization in the transport/sendmail/mod.rs file, creating a pathway for arbitrary command injection attacks. The lettre library serves as a comprehensive email sending library for rust applications, making this vulnerability particularly concerning as it affects a widely used component in email processing systems across various software implementations.
The technical flaw manifests through improper handling of user-supplied data within the sendmail transport mechanism. When applications utilize lettre to send emails through sendmail, the library fails to properly escape or validate command-line arguments that are passed to the underlying sendmail executable. This oversight creates a classic command injection vulnerability where malicious actors can inject arbitrary sendmail options and commands by manipulating input parameters. The vulnerability specifically impacts the transport layer that interfaces with the sendmail binary, allowing attackers to execute unintended commands with the privileges of the process running the lettre library.
The operational impact of this vulnerability extends beyond simple command execution, as it can lead to complete system compromise when applications using lettre are deployed in production environments. Attackers could potentially escalate privileges, access sensitive data, or disrupt services by injecting malicious sendmail options that modify the behavior of the underlying email delivery mechanism. The vulnerability affects any application that relies on lettre for email functionality and utilizes the sendmail transport method, particularly those running on systems where sendmail is available and accessible. This creates a significant risk for web applications, automated systems, and any software that processes user input through email sending functionality.
Mitigation strategies for CVE-2020-28247 should prioritize immediate upgrading to lettre version 0.10.0 or later where the vulnerability has been addressed through proper input validation and sanitization. Organizations should implement comprehensive input validation at multiple layers, including application-level sanitization of email addresses and message content before they are passed to lettre's sendmail transport. The fix typically involves proper escaping of special characters and command-line arguments to prevent injection attacks. Additionally, system administrators should consider implementing network segmentation and access controls to limit exposure of systems running lettre applications, while monitoring for suspicious email delivery patterns that might indicate exploitation attempts. This vulnerability aligns with CWE-78, which specifically addresses OS Command Injection, and maps to ATT&CK technique T1059.001 for command and scripting interpreter, highlighting the need for comprehensive security controls across multiple defensive layers.
The broader implications of this vulnerability underscore the importance of proper input validation in email processing libraries and the critical nature of dependency security management. Applications using lettre should implement regular security audits of their dependencies and maintain up-to-date vulnerability scanning processes to identify and remediate similar issues before they can be exploited in production environments. Organizations should also consider alternative email transport mechanisms that do not rely on external binaries, reducing the attack surface and dependency on potentially vulnerable system components.