CVE-2026-113792: pypdf Infinite Loop Vulnerability in PdfWriter.find_outline_item
Summary
CVE-2026-113792: pypdf: Possible infinite loop in PdfWriter.find_outline_item. Affects pypdf versions < 6.20.1. Fixed in 6.20.1. How to fix ↓
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Background
pypdf is a Python library used for manipulating PDF files. It allows users to create, modify, and extract information from PDFs. The library is widely utilized for its ease of use and comprehensive features, including the ability to handle outlines in PDF documents. However, a recent vulnerability has been identified that can lead to an infinite loop when using the PdfWriter.find_outline_item method, potentially causing applications to hang or crash.
Vulnerability Detail
The vulnerability arises from a flaw in the PdfWriter.find_outline_item method, which can be exploited by an attacker to craft a specially designed PDF file. When this method is called on the crafted PDF, it can lead to an infinite loop, causing the application to become unresponsive. This issue is classified under CWE-835, indicating that it can lead to excessive resource consumption and denial of service.
How To Fix
Latest published version: 6.21.2 as of 22 Oct 2026
pip install --upgrade "pypdf==6.21.2"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
6.20.1
This is the first release that contains the fix.
pip install --upgrade "pypdf==6.20.1"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
If upgrading is not immediately possible, users can apply the changes from pull request #4188 on GitHub. This involves manually modifying the code in the PdfWriter class to prevent the infinite loop when processing outlines.
Conclusion
The pypdf library has a vulnerability that can lead to an infinite loop when processing certain PDF files. Users are advised to upgrade to version 6.20.1 to fix this issue. For those unable to upgrade immediately, a workaround is available through code modifications. Regular monitoring for vulnerabilities using tools like Vulert can help maintain application security.
See every vulnerability recorded for pypdf →
FAQ
The vulnerability allows for an infinite loop when the find_outline_item method is called on a specially crafted PDF, leading to application hangs.
You can use the Vulert playground at Vulert Scanner to check if your application is affected without needing to sign up.
The CVSS score of this vulnerability is 6.0, indicating a moderate severity level.
Yes, the vulnerability has been fixed in pypdf version 6.20.1. Users should upgrade to this version to mitigate the issue.
If an upgrade is not possible, you can apply the changes from pull request #4188 to mitigate the risk temporarily.
References
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