CVE-2017-17843 in Enigmail
Summary
by MITRE
An issue was discovered in Enigmail before 1.9.9 that allows remote attackers to trigger use of an intended public key for encryption, because incorrect regular expressions are used for extraction of an e-mail address from a comma-separated list, as demonstrated by a modified Full Name field and a homograph attack, aka TBE-01-002.
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Analysis
by VulDB Data Team • 01/19/2023
The vulnerability identified as CVE-2017-17843 represents a critical flaw in Enigmail version 1.9.8 and earlier, which is a popular email encryption plugin for Mozilla Thunderbird. This security issue stems from improper handling of email address extraction within the encryption process, creating a potential vector for sophisticated attacks that exploit the trust model of public key cryptography. The flaw specifically manifests in the regular expression patterns used to parse email addresses from comma-separated lists, which fail to properly validate the integrity of the extracted information.
The technical implementation of this vulnerability involves a flawed regular expression mechanism that processes email addresses when users configure their encryption settings. When an attacker crafts a malicious email address with a modified full name field, the incorrect regex patterns fail to properly isolate the intended email address from the comma-separated list, potentially causing the system to select an unintended public key for encryption operations. This behavior creates a homograph attack surface where attackers can exploit Unicode character similarities to craft deceptive email addresses that appear legitimate but resolve to different addresses than intended.
From an operational perspective, this vulnerability enables remote attackers to perform targeted encryption substitution attacks without requiring direct access to the victim's private keys or encryption infrastructure. The attack exploits the fundamental trust relationship between email addresses and public keys, allowing adversaries to redirect encrypted messages to unintended recipients while maintaining the appearance of legitimate communication. This type of attack falls under the ATT&CK framework's technique T1566 for credential access through social engineering and T1071 for application layer protocol usage, as it leverages email protocols and user trust in address validation.
The impact of this vulnerability extends beyond simple message interception, as it can facilitate more sophisticated attacks including man-in-the-middle scenarios where encrypted communications are silently redirected. The weakness directly correlates to CWE-20, which addresses improper input validation in software systems, and CWE-347, which deals with improper validation of certificates and cryptographic signatures. The vulnerability demonstrates how seemingly minor parsing issues can create significant security implications in cryptographic systems, where the integrity of address resolution directly impacts the security of the entire encryption chain.
Security mitigation strategies for this vulnerability require immediate patching to Enigmail version 1.9.9 or later, which implements corrected regular expression patterns for email address extraction. Organizations should also implement additional verification mechanisms for email addresses before encryption operations, including manual confirmation of recipient identities and implementation of email address validation policies. System administrators should monitor for suspicious email address modifications and consider implementing automated checks for potential homograph attacks. The remediation process should include comprehensive testing of email address parsing functionality to ensure that the corrected implementation properly handles edge cases and maintains the integrity of the encryption trust model.