# CVE-2026-84310: pypdf denial of service via malicious PDF outlines

Source: https://junglewise.ai/threats/cve-2026-84310-pypdf-denial-of-service-via-malicious-pdf-outlines  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-01. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-84310 · Severity: medium · CVSS 4 · Published 2026-09-01

pypdf is a Python library used to process and manipulate PDF files. An attacker can craft a specially designed PDF with deeply nested or heavily duplicated outline entries that causes the library to consume excessive memory and CPU time when reading the document's outline (table of contents). This can lead to application hangs or crashes, disrupting any service that processes untrusted PDF files.

Technologies: [pypdf (PyPI)](https://junglewise.ai/threats/technologies/pypdf). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-84310 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-84310 being exploited in the wild.

**How severe is CVE-2026-84310?** Medium severity, with a CVSS score of 4, published 1 September 2026.

**Which products and versions are affected?** pypdf (PyPI) < 6.16.1, ECOSYSTEM:introduced=0,fixed=6.16.1.

**Is there a fix for CVE-2026-84310?** Yes. pypdf (PyPI): upgrade to 6.16.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-84310 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-84310?** Check whether you run pypdf (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- pypdf (PyPI): upgrade to 6.16.1 or later

  ```sh
  pip install "pypdf>=6.16.1"
  ```


## Technical details

This vulnerability is a denial-of-service (DoS) condition caused by asymmetric resource consumption and excessive iteration (CWE-405, CWE-834) in the outline parsing logic. When pypdf retrieves a document's outlines (bookmarks/table of contents), it does not adequately limit iteration depth or detect re-used nesting paths, allowing an attacker to craft a PDF that triggers quadratic or exponential processing time. The attack requires only local file access or the ability to supply a malicious PDF to an application; no authentication or user interaction beyond the victim opening/processing the file is needed. The affected versions are prior to 6.16.1, where the issue was remediated. A patch is available, and the fix was implemented in commit d91ab70.

## Affected products

- py-pdf pypdf < 6.16.1

## Identifiers

- CVE-2026-84310
- GHSA-23w6-3w8w-8484
- PYSEC-2026-3910

## Timeline

- 2026-09-01: disclosed
- 2026-09-01: patched: Fixed in pypdf 6.16.1

## References

- [https://api.github.com/users/stefan6419846](https://api.github.com/users/stefan6419846)
- [https://github.com/stefan6419846](https://github.com/stefan6419846)
- [https://api.github.com/users/stefan6419846/gists%7B/gist_id%7D](https://api.github.com/users/stefan6419846/gists%7B/gist_id%7D)
- [https://api.github.com/users/stefan6419846/repos](https://api.github.com/users/stefan6419846/repos)
- [https://avatars.githubusercontent.com/u/96178532?v=4](https://avatars.githubusercontent.com/u/96178532?v=4)
- [https://api.github.com/users/stefan6419846/events%7B/privacy%7D](https://api.github.com/users/stefan6419846/events%7B/privacy%7D)

## Related threats

- [pypdf memory exhaustion in cross-reference stream parsing](https://junglewise.ai/threats/cve-2026-119209-pypdf-is-a-free-and-open-source-pure-python-pdf-library-prior-to)
- [pypdf denial of service via forged encrypted PDF page count](https://junglewise.ai/threats/cve-2026-119208-pypdf-is-a-free-and-open-source-pure-python-pdf-library-prior-to)
- [pypdf excessive memory consumption in strict mode PDF parsing](https://junglewise.ai/threats/cve-2026-119207-pypdf-is-a-free-and-open-source-pure-python-pdf-library-prior-to)
- [pypdf denial of service via crafted page labels](https://junglewise.ai/threats/cve-2026-119206-pypdf-is-a-free-and-open-source-pure-python-pdf-library-prior-to)
- [pypdf infinite loop in DictionaryObject cloning](https://junglewise.ai/threats/cve-2026-119205-pypdf-is-a-free-and-open-source-pure-python-pdf-library-prior-to)