CVE-2026-27628 identifies a vulnerability in the pypdf library, a widely used pure-Python PDF processing tool. The flaw is classified under CWE-835, indicating a loop with an unreachable exit condition, effectively causing an infinite loop when processing certain crafted PDF files. This infinite loop occurs during the reading phase of the PDF, which means that any application or service using pypdf versions earlier than 6.7.2 to parse or manipulate PDFs could be forced into a hang state by an attacker supplying a maliciously crafted PDF. The vulnerability does not require any privileges or authentication but does require user interaction to trigger, such as opening or processing the malicious PDF file. The CVSS 4.0 base score is 1.2, reflecting a low severity primarily due to the limited impact (denial of service via application hang) and the need for user interaction. No known exploits have been reported in the wild, and the issue was publicly disclosed and fixed in version 6.7.2 of pypdf. Mitigation involves upgrading to the patched version or applying the patch manually if upgrading is not immediately feasible.

The primary impact of this vulnerability is a denial of service condition caused by an infinite loop, which can cause applications or services relying on pypdf to become unresponsive or consume excessive CPU resources. This can disrupt automated PDF processing workflows, web services that parse PDFs, or any software that integrates pypdf for PDF manipulation. While this does not lead to code execution or data leakage, the denial of service can affect availability and operational continuity, especially in environments processing large volumes of PDFs or handling untrusted documents. Organizations that rely on pypdf in critical systems may experience service degradation or outages if targeted. Since exploitation requires user interaction, the risk is mitigated somewhat by controlled document sources, but environments that accept PDFs from external or untrusted sources remain vulnerable.

Organizations should upgrade all instances of pypdf to version 6.7.2 or later to fully remediate this vulnerability. If immediate upgrading is not possible, applying the official patch manually is recommended. Additionally, implement strict input validation and sandboxing when processing PDFs from untrusted sources to limit the impact of potential infinite loops. Monitoring CPU and memory usage of PDF processing services can help detect abnormal behavior indicative of exploitation attempts. Employing rate limiting and timeouts on PDF parsing operations can prevent prolonged resource consumption. Educate users and administrators about the risks of opening PDFs from untrusted sources, and consider using alternative PDF libraries with robust security track records in high-risk environments.