CVE-2024-53920 is a vulnerability identified in the elisp-mode.el component of GNU Emacs versions prior to 30.1. The flaw occurs when a user invokes the elisp-completion-at-point function or enables on-the-fly diagnosis features that byte-compile Emacs Lisp source code from untrusted origins. These actions cause unsafe macro expansions within the Lisp interpreter, which can be exploited by attackers to execute arbitrary code on the victim's system. The vulnerability is classified under CWE-94 (Improper Control of Generation of Code), indicating that untrusted input is improperly handled, leading to code injection risks. The CVSS v3.1 score of 7.8 (high) reflects the vulnerability's significant impact on confidentiality, integrity, and availability, with an attack vector requiring local access (AV:L), low attack complexity (AC:L), no privileges required (PR:N), but user interaction (UI:R). The scope is unchanged (S:U), meaning the impact is confined to the vulnerable component's privileges. Although no exploits are known in the wild, the risk is substantial for users who open or interact with untrusted Emacs Lisp code. This vulnerability is particularly relevant for developers and researchers who use Emacs for Lisp development and may inadvertently process malicious code. The lack of a patch link suggests that users should upgrade to Emacs 30.1 or later, where this issue is resolved. The vulnerability underscores the risks of executing or processing untrusted code in extensible editors like Emacs.

The vulnerability allows attackers to execute arbitrary code on systems running vulnerable versions of GNU Emacs when users interact with untrusted Emacs Lisp source code. This can lead to full compromise of the affected system, including unauthorized data access, modification, or destruction, and potential disruption of services relying on Emacs. For European organizations, especially those in software development, academia, and research sectors where Emacs is commonly used, this poses a significant risk. Compromise could lead to intellectual property theft, disruption of development workflows, and potential lateral movement within networks. Since exploitation requires local access and user interaction, the threat is more pronounced in environments where users might open untrusted Lisp code, such as shared development environments or when handling third-party code. The vulnerability could also be leveraged in targeted attacks against organizations that rely heavily on Emacs for automation or scripting, increasing the potential impact on confidentiality, integrity, and availability.

1. Upgrade GNU Emacs to version 30.1 or later, where this vulnerability is fixed. 2. Avoid invoking elisp-completion-at-point or enabling on-the-fly diagnosis features on untrusted Emacs Lisp source code. 3. Implement strict policies to restrict the opening or byte-compiling of untrusted Lisp code within Emacs environments. 4. Educate users about the risks of interacting with untrusted Emacs Lisp code and enforce best practices for code review and source verification. 5. Use sandboxing or containerization techniques to isolate Emacs sessions when working with potentially untrusted code. 6. Monitor and audit Emacs usage logs to detect unusual activity related to Lisp code completion or compilation. 7. Employ endpoint protection solutions that can detect suspicious behavior resulting from code execution within Emacs processes. 8. Limit local user privileges to reduce the impact of potential exploitation.