CVE-2018-15586 in Enigmail
Summary
by MITRE
Enigmail before 2.0.6 is prone to to OpenPGP signatures being spoofed for arbitrary messages using a PGP/INLINE signature wrapped within a specially crafted multipart HTML email.
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Analysis
by VulDB Data Team • 07/09/2023
The vulnerability identified as CVE-2018-15586 affects Enigmail versions prior to 2.0.6, representing a critical security flaw in email encryption software that undermines the integrity of OpenPGP digital signatures. This vulnerability specifically targets the handling of PGP/INLINE signatures within multipart HTML email structures, creating a sophisticated attack vector that allows adversaries to forge digital signatures for arbitrary messages. The flaw exploits the way Enigmail processes email content when signatures are embedded within HTML multipart messages, potentially enabling man-in-the-middle attacks where malicious actors can manipulate signed communications without detection.
The technical root cause of this vulnerability lies in Enigmail's insufficient validation mechanisms when processing multipart email messages containing PGP/INLINE signatures. When an email contains both HTML content and OpenPGP signatures, the software fails to properly verify that the signature corresponds to the actual message content being displayed. This weakness stems from improper parsing of the multipart structure where the signature validation process does not adequately cross-reference the signature with the message body, particularly when HTML content is present. The vulnerability specifically manifests when a malicious actor crafts a multipart HTML email that includes a PGP/INLINE signature wrapping a different message than what is actually signed, allowing them to present a forged signature for content they did not originally sign.
The operational impact of this vulnerability extends beyond simple signature spoofing, creating potential risks for email security and trust mechanisms that rely on OpenPGP encryption. Attackers can exploit this flaw to make users believe they are receiving legitimate signed messages when in fact the signatures are forged, undermining the fundamental security properties that digital signatures are designed to provide. This vulnerability particularly affects email clients that use Enigmail for PGP encryption, potentially compromising sensitive communications in corporate environments, government agencies, and any organization relying on email-based digital signatures for authentication and integrity verification. The attack can be executed without requiring advanced technical skills, making it a significant threat to email security practices across various industries.
Organizations and users affected by this vulnerability should immediately upgrade to Enigmail version 2.0.6 or later, which includes patched validation mechanisms that properly handle multipart HTML email structures. The mitigation strategy should also include enhanced email security monitoring to detect suspicious signature patterns and regular security audits of email encryption practices. Security teams should implement additional verification steps when processing signed emails, particularly those containing HTML content, and consider deploying email security solutions that can detect and flag potentially malformed signature structures. This vulnerability aligns with CWE-225, which addresses weaknesses in input validation, and represents a specific implementation flaw in signature verification that could be categorized under ATT&CK technique T1566 for social engineering through email manipulation. The patched version addresses the core validation logic to ensure that PGP/INLINE signatures are properly associated with their corresponding message content regardless of the email's multipart structure.