CVE-2024-56520 is a vulnerability identified in the TCPDF library, a widely used PHP class for generating PDF documents. The flaw resides in the tc-lib-pdf-font component prior to version 2.6.4, which TCPDF versions before 6.8.0 incorporate. The vulnerability stems from improper parsing of font data, specifically the FontBBox attribute in Type 1 and TrueType fonts. FontBBox defines the bounding box of a font glyph, and mishandling this data can lead to incorrect font rendering or potentially malformed PDF structures. This misparsing can be exploited remotely without requiring authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). The impact includes potential confidentiality breaches (e.g., information leakage through crafted PDFs), integrity violations (e.g., document tampering or injection of malicious content), and availability issues (e.g., denial of service by crashing PDF processing systems). The vulnerability has a CVSS v3.1 score of 7.3, categorizing it as high severity. Although no public exploits have been reported yet, the widespread use of TCPDF in web applications and document management systems makes this a significant risk. The vulnerability affects any product or service embedding the vulnerable TCPDF versions, necessitating prompt remediation to prevent exploitation.

For European organizations, the vulnerability poses risks across multiple sectors that rely on PDF generation and processing, including government agencies, financial institutions, healthcare providers, and software vendors. Exploitation could lead to unauthorized disclosure of sensitive information embedded in PDFs, manipulation of official documents, or disruption of services dependent on PDF workflows. Given the remote and unauthenticated nature of the exploit, attackers could leverage this vulnerability to compromise web applications or backend systems that generate or handle PDFs, potentially leading to broader network infiltration or data breaches. The impact is heightened in environments where PDF documents are used for critical communications, contracts, or regulatory compliance. Additionally, denial of service conditions could disrupt business operations or public services. The lack of known exploits currently provides a window for proactive defense, but the high CVSS score indicates a strong likelihood of future exploit development.

European organizations should immediately assess their use of TCPDF and tc-lib-pdf-font components, identifying any instances of versions prior to TCPDF 6.8.0 and tc-lib-pdf-font 2.6.4. The primary mitigation is to upgrade these libraries to the fixed versions or later. Where upgrading is not immediately feasible, organizations should implement strict input validation and sanitization on PDF font data, restrict PDF generation to trusted sources, and monitor PDF processing logs for anomalies. Employing web application firewalls (WAFs) with rules targeting malformed PDF payloads may provide temporary protection. Security teams should also review document handling workflows to detect suspicious activity and ensure that PDF generation services run with least privilege. Regular vulnerability scanning and patch management processes should be reinforced to prevent exploitation. Finally, organizations should stay informed about any emerging exploit reports related to this vulnerability to adjust defenses accordingly.