CVE-2025-2866 is a vulnerability identified in The Document Foundation's LibreOffice software, specifically affecting versions 24.8 before 24.8.6 and 25.2 before 25.2.2. The issue stems from improper verification of cryptographic signatures, classified under CWE-347 (Improper Verification of Cryptographic Signature). The vulnerability concerns the handling of PDF digital signatures using the adbe.pkcs7.sha1 signature method. Due to a flaw in the verification logic, LibreOffice may incorrectly accept invalid or spoofed signatures as valid. This signature spoofing can mislead users into trusting documents that have been tampered with or forged, undermining the integrity and authenticity assurances typically provided by digital signatures. The vulnerability requires local access (AV:L) with low privileges (PR:L) and user interaction (UI:P) to exploit, as indicated by the CVSS 4.0 vector. The attack complexity is low (AC:L), but the impact on confidentiality, integrity, and availability is limited to low (VC:L, VI:N, VA:N). No known exploits are currently reported in the wild. The flaw primarily affects the integrity of document verification processes within LibreOffice's PDF handling, potentially enabling attackers to present malicious or altered documents as legitimately signed. This could have implications for workflows relying on LibreOffice for document validation and signing, especially in environments where document authenticity is critical.

For European organizations, the impact of this vulnerability is primarily related to the risk of accepting forged or tampered PDF documents as authentic. This can undermine trust in document workflows, particularly in sectors such as legal, financial, governmental, and healthcare, where document signatures are used to verify authenticity and compliance. While the vulnerability does not directly compromise confidentiality or availability, the integrity breach could facilitate social engineering, fraud, or unauthorized approvals based on falsified documents. Organizations relying heavily on LibreOffice for document processing and signature verification may face increased risk of document forgery going undetected. However, the low CVSS score and requirement for local access and user interaction reduce the likelihood of widespread exploitation. The absence of known exploits in the wild further limits immediate risk. Nonetheless, the vulnerability could be leveraged in targeted attacks or insider threat scenarios where an attacker has some level of system access and can trick users into opening maliciously crafted PDF files.

1. Immediate upgrade to LibreOffice versions 24.8.6 or later, or 25.2.2 or later, where the vulnerability has been patched, is the most effective mitigation. 2. Implement strict document handling policies that restrict opening PDF files from untrusted or unknown sources within LibreOffice, especially those purporting to have digital signatures. 3. Use alternative, dedicated PDF signature verification tools with robust cryptographic validation for critical workflows, rather than relying solely on LibreOffice's built-in verification. 4. Educate users on the risks of signature spoofing and the importance of verifying document provenance through multiple channels before acting on signed documents. 5. Employ endpoint security solutions that can detect and block attempts to open suspicious or malformed PDF files locally. 6. Monitor for unusual document-related activities or user behavior that might indicate exploitation attempts, such as unexpected signature validation failures or acceptance of dubious documents. 7. For environments with high security requirements, consider disabling PDF signature verification in LibreOffice until patched versions are deployed, if feasible.