CVE-2026-27628 identifies a vulnerability in the pypdf library, a pure-Python PDF processing tool widely used for reading and manipulating PDF files. The flaw is categorized under CWE-835, which involves a loop with an unreachable exit condition, effectively causing an infinite loop. In this case, an attacker can craft a malicious PDF file that triggers this infinite loop when parsed by vulnerable versions of pypdf (versions earlier than 6.7.2). The infinite loop occurs during the reading phase of the PDF, causing the application or service using pypdf to hang indefinitely, leading to denial of service (DoS). The attack vector requires the victim to open or process the crafted PDF, implying user interaction is necessary. No authentication or privileges are required to exploit this vulnerability. The CVSS 4.0 base score is 1.2, reflecting low severity due to limited impact and exploitation complexity. The vulnerability was publicly disclosed on February 25, 2026, and has been addressed in pypdf 6.7.2. While no known exploits have been reported in the wild, the vulnerability poses a risk to any system that automatically processes untrusted PDF files using vulnerable pypdf versions.

The primary impact of this vulnerability is denial of service through application hang or resource exhaustion caused by the infinite loop. Organizations that use pypdf to process PDFs—such as document management systems, automated PDF parsers, or web applications handling PDF uploads—may experience service disruptions or degraded performance when processing malicious PDFs. This can affect availability and potentially lead to operational downtime or degraded user experience. Since the vulnerability does not allow code execution or data leakage, confidentiality and integrity impacts are minimal. However, the disruption caused by the infinite loop can be exploited by attackers to target critical services that rely on pypdf, especially in automated workflows or batch processing environments. The lack of known exploits reduces immediate risk, but the ease of triggering the infinite loop by simply opening a crafted PDF means the threat should not be ignored.

The most effective mitigation is to upgrade pypdf to version 6.7.2 or later, where this vulnerability has been fixed. If upgrading is not immediately feasible, users should manually apply the patch provided by the pypdf maintainers to correct the infinite loop condition. Additionally, organizations should implement input validation and sandboxing for PDF processing to isolate and limit the impact of malicious files. Restricting PDF processing to trusted sources and scanning incoming PDFs with security tools can reduce exposure. Monitoring application performance and setting timeouts or resource limits on PDF parsing operations can help detect and mitigate hangs caused by infinite loops. Finally, educating users about the risks of opening untrusted PDFs and enforcing strict file upload policies can reduce the likelihood of exploitation.