If you are using TCPDF version <= 6.6.5, buckle up. The vulnerability CVE-2024-22640, which has recently come to light, holds the potential to wreak havoc on your security. TCPDF is a widely used PHP library for generating PDF documents, and this newfound ReDoS (Regular Expression Denial of Service) vulnerability could affect a large number of users.
In this long-read post, we will dive into the details of CVE-2024-22640, examining its implications and offering potential solutions to keep your system safe.
Background
TCPDF, a popular open-source PHP class for creating PDF files, has a history dating back to 2002. Thousands of software platforms, applications, and systems use TCPDF to handle their PDF document needs. Unfortunately, a newly discovered vulnerability in this critical library has placed many of these systems at risk. CVE-2024-22640 targets systems running TCPDF version <=6.6.5 and jeopardizes their security by exploiting a ReDoS vulnerability when parsing untrusted HTML pages with a crafted color.
The Exploit: ReDoS in TCPDF <=6.6.5
The vulnerability CVE-2024-22640 can be exploited by an attacker targeting systems that parse untrusted HTML pages with TCPDF <=6.6.5. By crafting a specific color in an HTML page, an attacker can trigger a Regular Expression Denial of Service (ReDoS) attack, which essentially blocks the system and creates a denial-of-service condition. This can further allow the attacker to consume system resources and disrupt the normal operation of the target.
When parsing an HTML page, TCPDF handles colors using regular expressions. The faulty regex implementation causes the vulnerability. For instance, if an attacker supplies an HTML page containing the following color string:
#010101010101010101010101010101010101010101010101010101+/rgb://-000000 and the affected version < 6.6.5'
The flawed regex implementation in TCPDF struggles to process the color string above, leading to an exponential increase in CPU usage, ultimately causing a ReDoS attack and bringing the target system to a standstill.
References
The vulnerability was initially reported on the GitHub issue tracking system for TCPDF. You can check the original reference containing the vulnerability details, PoC, and relevant discussion at the following link:
Original GitHub Reference
The Common Vulnerabilities and Exposures (CVE) reference can be found here
A Real-World Scenario
It is essential to understand the practical ramifications of CVE-2024-22640. To grasp the severity, let's consider a real-world scenario: an online invoicing application that uses TCPDF <=6.6.5 to generate PDF invoices.
In this case, a malicious user could forge an invoice, embed a crafted color string (similar to the provided example), and upload it to the invoicing application. As the application ingests the untrusted HTML page content and tries to render a PDF invoice, the ReDoS vulnerability would be triggered, potentially taking down the application and disrupting critical operations.
Preventing the Attack
Given the significant potential impact of CVE-2024-22640, it is vital to take necessary precautions. To prevent the ReDoS attack and protect your system, consider the following recommendations:
1. Upgrade to TCPDF 6.6.6+: Upgrade your TCPDF library to a version >= 6.6.6 to patch the vulnerability.
2. Limit Untrusted HTML Input: Restrict or sanitize untrusted user input (e.g., colors) when generating PDFs.
Conclusion
CVE-2024-22640 is a severe vulnerability in TCPDF versions <=6.6.5. Its exploitation could result in ReDoS attacks, causing significant system downtime and performance degradation. To safeguard your system, ensure your TCPDF implementation is updated to the latest version and be cautious when dealing with untrusted HTML input.
Stay vigilant and keep an eye on any new vulnerabilities impacting your system. Regularly check the CVE database and the TCPDF repository to stay informed about any new threats and updates.
Timeline
Published on: 04/19/2024 16:15:09 UTC
Last modified on: 07/03/2024 01:47:19 UTC