CVE-2024-22640 identifies a Regular Expression Denial of Service (ReDoS) vulnerability in TCPDF, a widely used PHP library for generating PDF documents from HTML content. Versions up to and including 6.6.5 are vulnerable. The issue stems from the way TCPDF parses color attributes within HTML input using inefficient regular expressions. When an attacker supplies a crafted color value, the regex engine experiences catastrophic backtracking, consuming excessive CPU cycles and causing the application to become unresponsive or significantly degraded in performance. This vulnerability does not require any privileges or user interaction, making it remotely exploitable over the network. The impact is limited to availability (denial of service), with no direct compromise of data confidentiality or integrity. No known public exploits have been reported yet, but the vulnerability is rated high severity with a CVSS v3.1 score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). The underlying weakness corresponds to CWE-1333, which relates to ReDoS conditions caused by vulnerable regular expressions. Since TCPDF is commonly embedded in web applications to convert HTML to PDF, any service accepting untrusted HTML input and using affected TCPDF versions is susceptible to this attack. The absence of a patch link suggests that a fix may still be pending or not yet widely distributed, emphasizing the need for interim mitigations.

For European organizations, the primary impact of this vulnerability is service availability disruption. Organizations that rely on TCPDF for dynamic PDF generation from user-supplied or external HTML content—such as government portals, financial institutions, healthcare providers, and e-commerce platforms—may experience denial of service conditions if targeted. This could lead to downtime, degraded user experience, and operational delays. While no data breach or integrity compromise is directly associated, prolonged or repeated outages could erode trust and cause financial losses. Additionally, automated systems that generate reports or documents on demand could be interrupted, affecting business continuity. The vulnerability's remote exploitability without authentication increases the attack surface, especially for public-facing services. Given the widespread use of PHP and TCPDF in Europe, the threat is relevant across multiple sectors. Organizations with stringent uptime requirements or those subject to regulatory compliance around service availability (e.g., financial and healthcare sectors) face heightened risk.

1. Monitor TCPDF project repositories and security advisories for official patches addressing CVE-2024-22640 and apply updates promptly once available. 2. In the interim, implement strict input validation and sanitization to reject or neutralize suspicious or malformed color attributes in HTML content before processing. 3. Employ rate limiting and request throttling on endpoints that accept HTML input to reduce the risk of resource exhaustion from repeated exploit attempts. 4. Consider isolating PDF generation services in separate containers or sandboxed environments to limit the impact of potential denial of service. 5. Use Web Application Firewalls (WAFs) with custom rules to detect and block suspicious payloads targeting the vulnerable regex patterns if signatures become available. 6. Audit and restrict access to PDF generation functionality to trusted users or internal systems where feasible. 7. Conduct performance monitoring and alerting on CPU usage spikes in services utilizing TCPDF to enable rapid detection of exploitation attempts. 8. Review and update incident response plans to include scenarios involving ReDoS attacks on document generation services.