CVE-2026-54531
Summary
by MITRE • 06/23/2026
pypdf is a free and open-source pure-python PDF library. Prior to 6.13.0, an attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This requires merging a file with outlines into a writer. This vulnerability is fixed in 6.13.0.
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Analysis
by VulDB Data Team • 06/23/2026
The pypdf library presents a critical security vulnerability that affects versions prior to 6.13.0, specifically targeting the library's handling of PDF files containing outlines or bookmarks. This flaw manifests as an infinite loop condition that can be exploited by malicious actors who craft specially formatted PDF documents. The vulnerability occurs during the file merging process when a PDF with outlines is combined with another document using the writer functionality. The technical implementation of this issue stems from inadequate boundary checking and loop termination conditions within the library's outline processing code, which fails to properly validate the structure of incoming PDF data containing nested or recursive outline references.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it creates a denial-of-service condition that can consume system resources indefinitely. Attackers can exploit this weakness by preparing a malicious PDF file with malformed outline structures that trigger the infinite loop during the merge operation. This type of vulnerability aligns with CWE-835, which addresses the issue of loops with insufficient termination conditions, and represents a classic example of a resource exhaustion attack that can be leveraged to disrupt services. The vulnerability affects any application or system that utilizes pypdf for PDF manipulation, particularly those that process user-uploaded documents or merge multiple PDF files together.
Security practitioners should prioritize updating to pypdf version 6.13.0 or later, as this release includes the necessary patches to prevent the infinite loop condition during outline processing. The fix implemented in version 6.13.0 addresses the core issue by introducing proper validation checks and robust loop termination mechanisms when handling PDF outlines. Organizations using older versions of pypdf should implement immediate mitigations such as input sanitization, PDF file validation before processing, and limiting the scope of file merging operations. Additionally, monitoring for unusual resource consumption patterns during PDF processing operations can help detect potential exploitation attempts. From an attack surface perspective, this vulnerability maps to ATT&CK technique T1499.004, which covers resource exhaustion attacks through manipulation of data processing loops, making it particularly concerning for environments where automated PDF processing is common.