CVE-2026-27888 is a vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) affecting the pypdf library, a widely used pure-Python PDF processing tool. Versions of pypdf prior to 6.7.3 are susceptible to this issue. The vulnerability arises when an attacker crafts a specially designed PDF file containing an XFA (XML Forms Architecture) stream compressed with the /FlateDecode filter. When the vulnerable pypdf library accesses the 'xfa' property of a PDF reader or writer object, it triggers excessive memory allocation due to improper handling of the compressed stream, leading to RAM exhaustion. This can cause the application or service using pypdf to crash or become unresponsive, effectively resulting in a denial of service (DoS). The vulnerability does not require any authentication or user interaction and can be exploited remotely by simply processing the malicious PDF file. The CVSS v4.0 base score is 6.6, reflecting a medium severity with network attack vector, low attack complexity, no privileges or user interaction required, and a high impact on availability. The issue was publicly disclosed on February 26, 2026, and fixed in pypdf version 6.7.3. No known exploits have been reported in the wild, but the vulnerability poses a risk to any system that automatically processes untrusted PDF files using affected pypdf versions. The recommended mitigation is to upgrade to pypdf 6.7.3 or later, or apply the patch manually if immediate upgrade is not feasible.

The primary impact of CVE-2026-27888 is denial of service through resource exhaustion. Organizations that use pypdf to process PDFs—such as document management systems, web applications handling PDF uploads, automated PDF parsing services, or any backend system integrating pypdf—may experience application crashes or service outages when processing maliciously crafted PDFs. This can disrupt business operations, degrade user experience, and potentially lead to cascading failures if the affected service is critical. Although the vulnerability does not directly compromise confidentiality or integrity, the availability impact can be significant, especially in environments with high PDF processing volumes or automated workflows. Attackers can exploit this vulnerability remotely without authentication, increasing the risk of widespread disruption. The lack of known exploits in the wild suggests limited active exploitation currently, but the ease of exploitation and medium severity warrant proactive mitigation. Organizations relying on pypdf in security-sensitive or high-availability contexts should treat this vulnerability seriously to avoid operational disruptions.

To mitigate CVE-2026-27888, organizations should immediately upgrade all instances of pypdf to version 6.7.3 or later, where the vulnerability is fixed. If upgrading is not immediately possible, apply the official patch manually to the affected versions to prevent exploitation. Additionally, implement input validation and filtering to restrict or sanitize PDF files before processing, especially from untrusted sources. Employ resource usage monitoring and limits on PDF processing services to detect and mitigate abnormal memory consumption patterns indicative of exploitation attempts. Consider sandboxing PDF processing components to isolate failures and prevent service-wide impact. Maintain up-to-date software inventories to identify all systems using pypdf and prioritize patching accordingly. Finally, monitor security advisories and threat intelligence feeds for any emerging exploit activity related to this vulnerability.