The vulnerability identified as CVE-2026-27024 affects the py-pdf pypdf library, a pure-Python PDF processing library widely used for reading and manipulating PDF files. The flaw is classified under CWE-835, which pertains to loops with unreachable exit conditions, commonly resulting in infinite loops. Specifically, the issue arises when the library processes the children of a TreeObject within a PDF document, such as when handling outlines or bookmarks. An attacker can craft a malicious PDF file that triggers this infinite loop during parsing, causing the application to hang indefinitely. This can lead to denial of service (DoS) conditions in any software or service that uses the vulnerable pypdf versions below 6.7.1. The vulnerability does not require authentication, user interaction, or elevated privileges, but exploitation requires the application to parse the malicious PDF. The CVSS v4.0 score is 6.9 (medium severity), reflecting local attack vector, low complexity, no privileges or user interaction required, and a high impact on availability. The vulnerability was publicly disclosed and fixed in version 6.7.1 of pypdf. No known active exploits have been reported to date. This vulnerability primarily affects software environments that rely on pypdf for PDF processing, including document management systems, web applications, and automated PDF workflows.

The primary impact of CVE-2026-27024 is denial of service due to an infinite loop triggered by maliciously crafted PDFs. Organizations that use pypdf in automated document processing, web services, or desktop applications risk service disruption or application hangs when processing untrusted PDF files. This can degrade user experience, cause downtime, or require manual intervention to recover. While the vulnerability does not lead to code execution or data leakage, the availability impact can be significant in environments processing large volumes of PDFs or exposed to untrusted inputs. Attackers could exploit this to disrupt business operations, particularly in sectors relying heavily on PDF workflows such as legal, finance, publishing, and government. Since exploitation does not require authentication or user interaction, any exposed PDF processing endpoint or service is potentially vulnerable. The lack of known exploits suggests limited current threat but the medium severity score and ease of triggering the infinite loop warrant prompt mitigation.

To mitigate CVE-2026-27024, organizations should 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 sandboxing to isolate PDF processing tasks and prevent resource exhaustion. Limit the size and complexity of PDFs accepted from untrusted sources. Employ timeout mechanisms or watchdog processes to detect and terminate hung PDF parsing operations. Monitor logs for repeated processing failures or unusually long processing times indicative of infinite loops. Additionally, restrict access to PDF processing services to trusted users or networks to reduce exposure. Regularly review and update dependencies to incorporate security patches promptly. Finally, consider alternative PDF libraries with robust security track records if pypdf is not essential.