CVE-2017-14482 in Emacs
Summary
by MITRE
GNU Emacs before 25.3 allows remote attackers to execute arbitrary code via email with crafted "Content-Type: text/enriched" data containing an x-display XML element that specifies execution of shell commands, related to an unsafe text/enriched extension in lisp/textmodes/enriched.el, and unsafe Gnus support for enriched and richtext inline MIME objects in lisp/gnus/mm-view.el. In particular, an Emacs user can be instantly compromised by reading a crafted email message (or Usenet news article).
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Analysis
by VulDB Data Team • 12/29/2022
CVE-2017-14482 represents a critical remote code execution vulnerability affecting GNU Emacs versions prior to 25.3, demonstrating a dangerous intersection of email processing and XML parsing that enables attackers to execute arbitrary commands on vulnerable systems. This vulnerability exists within the text/enriched MIME content type handling mechanism, specifically in the lisp/textmodes/enriched.el file and the lisp/gnus/mm-view.el file that governs Gnus email client support for enriched and richtext inline MIME objects. The flaw stems from the improper handling of XML elements within email content, particularly the x-display element that can be embedded within text/enriched data streams, allowing malicious actors to craft specially formatted email messages that trigger unintended shell command execution when processed by vulnerable Emacs instances.
The technical implementation of this vulnerability exploits the unsafe parsing of XML elements within the enriched text format, where the x-display element serves as a command injection vector that bypasses normal input validation mechanisms. When GNU Emacs processes email messages containing crafted text/enriched content with malicious x-display XML elements, it fails to properly sanitize or validate the embedded XML structure, leading to arbitrary command execution with the privileges of the user running Emacs. This represents a classic sandbox escape vulnerability where the application's legitimate text processing capabilities become weaponized through improper XML handling, creating an attack surface that can be exploited simply by reading an email message without any additional user interaction beyond normal email consumption.
The operational impact of CVE-2017-14482 extends far beyond typical email-based attacks, as it can compromise systems through passive email reading activities that require no user confirmation or explicit interaction. This vulnerability aligns with ATT&CK technique T1204.002 for "User Execution: Malicious File" and demonstrates how email-based attacks can be elevated to full system compromise through improper content handling. The vulnerability affects not only individual users but also organizations that rely on Emacs for email processing, creating a significant risk for environments where Emacs is used as a primary email client or integrated into automated processing workflows. The immediate compromise occurs during the rendering of email content, making it particularly dangerous for users who may inadvertently read malicious emails, as the attack vector requires no additional user actions beyond normal email reading behavior.
Mitigation strategies for CVE-2017-14482 primarily focus on upgrading to GNU Emacs 25.3 or later versions where the vulnerability has been patched through proper XML element sanitization and input validation mechanisms. Organizations should implement email filtering solutions that can identify and block text/enriched MIME content types or apply additional layers of content filtering that sanitize email content before it reaches the Emacs client. The fix implemented in version 25.3 addresses the core issue by modifying the enriched text processing code to properly validate XML elements and prevent the execution of shell commands through malicious x-display elements, aligning with CWE-74 standards for input validation and CWE-94 standards for improper control of generation of code. System administrators should also consider implementing security awareness training to educate users about the risks of reading untrusted email content and establish policies that restrict the processing of potentially malicious email formats, particularly in high-value organizational environments where the compromise of a single user's Emacs instance could lead to broader network infiltration.