CVE-2026-27024 is a vulnerability classified under CWE-835 (Loop with Unreachable Exit Condition) affecting the py-pdf pypdf library, a widely used pure-Python PDF processing tool. Versions prior to 6.7.1 contain a flaw where an attacker can craft a malicious PDF file that causes the library to enter an infinite loop when accessing the children of a TreeObject, such as when processing PDF outlines. This infinite loop arises because the loop controlling the traversal of these children lacks a reachable exit condition under certain malformed inputs, causing the application to hang indefinitely. The vulnerability does not require any privileges, user interaction, or authentication, but does require that the vulnerable library processes the crafted PDF. The CVSS 4.0 score is 6.9 (medium severity), reflecting the local attack vector and the impact on availability (denial of service) without compromising confidentiality or integrity. No known exploits have been reported in the wild as of now. The issue was publicly disclosed on February 20, 2026, and fixed in pypdf version 6.7.1. This vulnerability is particularly relevant for applications and services that automatically parse or analyze untrusted PDF documents using pypdf, such as document management systems, PDF viewers, or automated PDF processing pipelines.

The primary impact of CVE-2026-27024 is a denial of service condition caused by an infinite loop, which can cause the affected application or service to become unresponsive or consume excessive CPU resources. This can disrupt business operations relying on automated PDF processing, potentially leading to downtime or degraded service availability. Since the vulnerability does not affect confidentiality or integrity, data leakage or tampering is not a direct concern. However, the denial of service can be exploited to disrupt workflows or as part of a larger attack chain. Organizations that integrate pypdf into their software stacks, especially those processing PDFs from untrusted sources, are at risk. The scope includes any system running vulnerable versions of pypdf, including servers, desktop applications, and cloud services that parse PDFs. The ease of exploitation is moderate since it requires supplying a crafted PDF to the vulnerable system, but no authentication or user interaction is needed, increasing the risk in automated environments.

To mitigate CVE-2026-27024, organizations should immediately upgrade all instances of the pypdf library to version 6.7.1 or later, where the infinite loop vulnerability is fixed. For environments where immediate upgrading is not feasible, implement input validation and filtering to block or quarantine suspicious or untrusted PDF files before processing. Employ resource limits and timeouts on PDF parsing operations to prevent infinite loops from causing prolonged service disruption. Monitor CPU and memory usage of PDF processing services to detect anomalous behavior indicative of exploitation attempts. Additionally, consider sandboxing PDF processing components to isolate potential denial of service impacts. Regularly review and update third-party dependencies to incorporate security patches promptly. Finally, maintain awareness of any emerging exploits or related vulnerabilities in PDF libraries to adapt defenses accordingly.