CVE-2023-6186: LibreOffice Macro Execution RCE Vulnerability

CVE-2023-6186 Overview

CVE-2023-6186 is an authorization bypass vulnerability affecting The Document Foundation's LibreOffice office suite. The vulnerability stems from insufficient macro permission validation, which allows an attacker to execute built-in macros without triggering the standard user warning prompts. In affected versions, LibreOffice supports hyperlinks with macro or similar built-in command targets that can be executed when activated without warning the user, effectively bypassing security controls designed to protect users from malicious macro execution.

Critical Impact

Attackers can execute built-in macros through crafted hyperlinks without user consent or warning, potentially leading to system compromise, data theft, or malware installation when users interact with malicious documents.

Affected Products

• LibreOffice (versions prior to patched releases)
• Fedora 38
• Debian Linux 11.0 and 12.0

Discovery Timeline

• December 11, 2023 - CVE-2023-6186 published to NVD
• February 13, 2025 - Last updated in NVD database

Technical Details for CVE-2023-6186

Vulnerability Analysis

This vulnerability is classified under CWE-281 (Improper Preservation of Permissions), indicating a fundamental flaw in how LibreOffice handles macro permission validation during hyperlink processing. The issue manifests when users interact with specially crafted documents containing hyperlinks that target built-in macro commands.

LibreOffice includes security mechanisms designed to warn users before executing macros, which is a critical defense against macro-based malware attacks. However, this vulnerability creates a bypass path where hyperlinks can invoke built-in macro functionality without triggering these protective warnings. This effectively circumvents the macro security model that users depend on to protect against malicious document-based attacks.

The vulnerability requires user interaction (clicking a malicious hyperlink within a document), but the lack of warning eliminates the user's opportunity to make an informed security decision. An attacker with low-level access can craft a malicious document and distribute it via phishing campaigns, email attachments, or other document-sharing mechanisms.

Root Cause

The root cause lies in insufficient validation logic within LibreOffice's hyperlink processing mechanism. When a hyperlink targets a built-in macro or similar command, the application fails to apply the same permission validation and user warning mechanisms that would normally be invoked for explicit macro execution requests. This permission preservation failure allows macro-like functionality to execute outside the normal security control path.

Attack Vector

The attack exploits the network-accessible nature of document distribution. An attacker crafts a LibreOffice document containing hyperlinks that target built-in macro commands. When the victim opens the document and clicks the malicious hyperlink, the associated macro commands execute without any security warning being displayed. The attack scenario follows this pattern:

1. Attacker creates a malicious LibreOffice document with crafted hyperlinks targeting built-in macro commands
2. Document is distributed to victims via email, file sharing, or web download
3. Victim opens the document in an affected LibreOffice version
4. Victim clicks on what appears to be a legitimate hyperlink
5. Built-in macro commands execute without warning, potentially compromising the system

Since no verified code examples are available for this vulnerability, readers should consult the LibreOffice Security Advisory for technical implementation details regarding the vulnerability mechanism and its exploitation characteristics.

Detection Methods for CVE-2023-6186

Indicators of Compromise

• Documents containing unusual hyperlink structures targeting internal macro commands or vnd.sun.star protocol handlers
• Unexpected LibreOffice process behavior following document interaction, such as spawned child processes or network connections
• Suspicious document files received from untrusted sources with embedded hyperlinks
• Unusual file system or registry modifications following document opening

Detection Strategies

• Monitor LibreOffice process execution for unexpected child process spawning after document opens
• Implement email gateway scanning for documents containing suspicious hyperlink patterns
• Deploy endpoint detection rules to identify macro-like behavior originating from hyperlink activation
• Review document metadata and content for indicators of embedded macro command hyperlinks

Monitoring Recommendations

• Enable enhanced logging for LibreOffice application events and document interactions
• Configure security information and event management (SIEM) rules to correlate document opens with subsequent suspicious activity
• Implement network monitoring for unexpected outbound connections following document interaction
• Monitor file system activity for changes triggered by LibreOffice processes

How to Mitigate CVE-2023-6186

Immediate Actions Required

• Update LibreOffice to the latest patched version immediately
• Review and apply security updates from distribution repositories (Debian, Fedora)
• Educate users about the risks of clicking hyperlinks in documents from untrusted sources
• Consider temporarily restricting document opening to trusted sources only

Patch Information

The Document Foundation has released security patches addressing this vulnerability. Users should update to the latest LibreOffice version through official channels or their distribution's package manager.

For detailed patch information and affected version ranges, refer to:

• LibreOffice Security Advisory CVE-2023-6186
• Debian Security Advisory DSA-5574
• Debian LTS Announcement
• Fedora Package Announcement

Workarounds

• Configure LibreOffice macro security to the highest level via Tools → Options → Security → Macro Security
• Disable hyperlink execution by holding Ctrl while clicking links (manual verification mode)
• Use document viewers instead of full LibreOffice for untrusted documents
• Implement organizational policies restricting document sources to trusted origins

# Update LibreOffice on Debian/Ubuntu systems
sudo apt update
sudo apt upgrade libreoffice

# Update LibreOffice on Fedora systems
sudo dnf update libreoffice

# Verify installed LibreOffice version
libreoffice --version