CVE-2024-5261: LibreOffice TLS Verification Vulnerability

CVE-2024-5261 Overview

CVE-2024-5261 is a critical Improper Certificate Validation vulnerability affecting LibreOffice when operating in "LibreOfficeKit" mode. This security flaw completely disables TLS certificate verification for network requests, exposing applications that embed LibreOffice functionality to man-in-the-middle attacks and other network-based exploits.

LibreOfficeKit is a C/C++ interface that allows third-party applications to leverage LibreOffice's document processing capabilities. This is commonly used for document conversion, viewing, and manipulation in enterprise applications and web services. The vulnerability stems from LibreOffice's use of the curl library to fetch remote resources such as images hosted on web servers. In affected versions, when LibreOffice operates in LibreOfficeKit mode, the CURLOPT_SSL_VERIFYPEER option was set to false, effectively disabling all TLS certificate validation.

Critical Impact

Complete bypass of TLS certificate verification enables attackers to intercept, modify, or inject malicious content during document processing operations without detection.

Affected Products

• LibreOffice versions prior to 24.2.4
• Applications using LibreOfficeKit for document processing
• Third-party document conversion services leveraging LibreOffice

Discovery Timeline

• June 25, 2024 - CVE-2024-5261 published to NVD
• December 23, 2025 - Last updated in NVD database

Technical Details for CVE-2024-5261

Vulnerability Analysis

This vulnerability represents a severe cryptographic weakness (CWE-295: Improper Certificate Validation) that undermines the fundamental security guarantees of TLS/SSL communications. When LibreOffice operates in LibreOfficeKit mode, it fails to verify the authenticity of remote servers when fetching external resources.

The flaw specifically affects the curl library integration within LibreOffice. During normal standalone operation, LibreOffice properly validates TLS certificates for all HTTPS connections. However, when the application is instantiated through the LibreOfficeKit API—commonly used in server-side document processing scenarios—this critical security check is bypassed entirely.

This creates a dangerous scenario where documents containing references to external resources (images, stylesheets, or other linked content) can be manipulated during transit. An attacker positioned on the network path between the LibreOfficeKit instance and the remote server can present a fraudulent certificate and intercept or modify the response without triggering any security warnings.

Root Cause

The root cause is the improper configuration of the curl library when LibreOffice initializes in LibreOfficeKit mode. The CURLOPT_SSL_VERIFYPEER option was explicitly set to false, which instructs curl to accept any TLS certificate regardless of its validity, expiration status, or chain of trust. This configuration error appears to have been introduced to simplify development or testing scenarios but was inadvertently included in production releases.

Attack Vector

The vulnerability is exploitable over the network without requiring any user interaction or authentication. An attacker can exploit this flaw through the following attack scenario:

1. A victim application uses LibreOfficeKit to process a document containing external resource references (e.g., remotely hosted images)
2. The attacker positions themselves on the network path (via ARP spoofing, DNS hijacking, compromised network infrastructure, or malicious Wi-Fi access point)
3. When LibreOfficeKit attempts to fetch the external resource via HTTPS, the attacker intercepts the request
4. The attacker presents their own certificate and responds with malicious content
5. Due to disabled certificate verification, LibreOfficeKit accepts the malicious response without validation
6. The attacker-controlled content is processed and potentially rendered or executed within the context of the document

This attack is particularly dangerous in cloud-based document conversion services, collaborative document editing platforms, and enterprise document management systems that rely on LibreOfficeKit for backend processing.

Detection Methods for CVE-2024-5261

Indicators of Compromise

• Unexpected TLS connection failures or certificate warnings in upstream proxies while LibreOfficeKit instances continue to operate normally
• Network traffic analysis showing HTTPS connections from LibreOfficeKit processes that do not validate server certificates
• Anomalous content in processed documents that differs from expected external resources
• Evidence of man-in-the-middle activity in network logs near document processing infrastructure

Detection Strategies

• Deploy network monitoring to detect TLS connections that accept invalid or self-signed certificates from LibreOffice processes
• Implement certificate pinning validation at the network perimeter for known external resources accessed by document processing systems
• Conduct regular software inventory audits to identify LibreOffice installations below version 24.2.4
• Use application-level logging to track external resource fetching behavior in LibreOfficeKit deployments

Monitoring Recommendations

• Enable verbose curl logging for LibreOfficeKit instances to capture certificate validation events
• Monitor for unexpected DNS queries or IP connections from document processing servers
• Implement TLS inspection at network boundaries to validate certificate chains for outbound connections
• Set up alerts for LibreOffice processes making HTTPS connections to untrusted or newly-registered domains

How to Mitigate CVE-2024-5261

Immediate Actions Required

• Upgrade all LibreOffice installations to version 24.2.4 or later immediately
• Audit all applications and services that utilize LibreOfficeKit for document processing
• Implement network segmentation to isolate document processing infrastructure from untrusted networks
• Review and restrict external network access for LibreOfficeKit instances where possible

Patch Information

LibreOffice has addressed this vulnerability in version 24.2.4 and later releases. The fix restores proper TLS certificate verification by setting CURLOPT_SSL_VERIFYPEER to true when operating in LibreOfficeKit mode, ensuring consistent security behavior across all deployment configurations.

Organizations should apply the update as soon as possible. The official security advisory is available at the LibreOffice Security Advisory page.

Workarounds

• Configure network firewalls to block or proxy all outbound HTTPS connections from LibreOfficeKit instances through a TLS-inspecting proxy that enforces certificate validation
• Process documents in isolated network environments without external internet access
• Pre-fetch and locally cache all external resources before document processing to eliminate runtime network requests
• Consider disabling external resource loading entirely in LibreOfficeKit configurations where feasible

# Verify LibreOffice version to confirm patched status
libreoffice --version
# Expected output should show version 24.2.4 or higher

# For containerized deployments, update base images
# Example: Pull updated LibreOffice container
docker pull libreoffice/libreoffice:24.2.4

# Network-level mitigation: Block direct external HTTPS from LibreOffice processes
# Force traffic through validating proxy (example iptables rule)
iptables -A OUTPUT -p tcp --dport 443 -m owner --uid-owner libreoffice -j REJECT