CVE-2026-27024: pypdf Infinite Loop Vulnerability in TreeObject Processing
Summary
CVE-2026-27024: pypdf has a possible infinite loop when processing TreeObject. Affects pypdf versions < 6.7.1. Fixed in 6.7.1. How to fix ↓
Also tracked for
The same CVE-2026-27024 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
pypdf is a popular Python library used for manipulating PDF files. It allows users to create, modify, and extract information from PDF documents. The library is widely utilized in various applications due to its ease of use and comprehensive functionality. However, it has a vulnerability that can lead to an infinite loop when processing certain PDF structures, specifically TreeObjects, which are often used in document outlines.
Vulnerability Detail
The vulnerability arises from the way pypdf handles TreeObjects. An attacker can craft a malicious PDF that, when processed, leads to an infinite loop. This occurs when the library attempts to access the children of a TreeObject, potentially causing the application to hang indefinitely. The implications of this vulnerability can be severe, as it may lead to denial of service, impacting the usability of applications that rely on pypdf for PDF processing.
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
6.7.1
This is the first release that contains the fix.
pip install --upgrade "pypdf==6.7.1"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
If you are unable to upgrade to the patched version immediately, you can apply the changes from pull request #3645. This involves modifying the code to handle TreeObject processing more safely. The specific changes can be found in the pull request on GitHub: https://github.com/py-pdf/pypdf/pull/3645.
Conclusion
The pypdf library has a vulnerability that can lead to an infinite loop when processing TreeObjects in PDFs. It is crucial for users to upgrade to version 6.7.1 to mitigate this risk. For those unable to upgrade immediately, applying the changes from the relevant pull request can serve as a temporary solution.
See every vulnerability recorded for pypdf →
FAQ
The vulnerability allows for an infinite loop when processing certain PDF structures, specifically TreeObjects.
You can use the Vulert playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
The main consequence is a denial of service, as the application may hang indefinitely when processing a malicious PDF.
Yes, the vulnerability has been fixed in pypdf version 6.7.1. It is recommended to upgrade to this version.
If you cannot upgrade, consider applying the changes from pull request #3645 as a temporary workaround.
References
Related vulnerabilities
Recent vulnerabilities recorded for pypdf.
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