# CVE-2023-36810: PYSEC-2026-1837 - PyPDF2 quadratic runtime with malformed PDF missing xref marker

Source: https://junglewise.ai/threats/cve-2023-36810-pypdf2-quadratic-runtime-with-malformed-pdf-missing-xref-marker  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-07  
License: CC BY 4.0 with a link back

CVE-2023-36810 · Severity: low · CVSS 3.1 · Published 2026-07-07

PyPDF2 quadratic runtime with malformed PDF missing xref marker

Technologies: [pypdf2 (PyPI)](https://junglewise.ai/threats/technologies/pypdf2). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2023-36810 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2023-36810 being exploited in the wild.

**How severe is CVE-2023-36810?** Low severity, with a CVSS score of 3.1, published 7 July 2026.

**Which products and versions are affected?** pypdf2 (PyPI) ECOSYSTEM:introduced=0,fixed=1.27.9.

**Is there a fix for CVE-2023-36810?** Yes. pypdf2 (PyPI): upgrade to 1.27.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2023-36810?** Check whether you run pypdf2 (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

- pypdf2 (PyPI): upgrade to 1.27.9 or later

  ```sh
  pip install "pypdf2>=1.27.9"
  ```


## Affected products

- pypdf2 (PyPI) ECOSYSTEM:introduced=0,fixed=1.27.9

## Identifiers

- CVE-2023-36810
- GHSA-jrm6-h9cq-8gqw
- PYSEC-2026-1837

## Related threats

- [PYSEC-2026-3008 - pypdf and PyPDF2 possible Infinite Loop when a comment isn't followed by a character](https://junglewise.ai/threats/cve-2023-36464-pypdf-and-pypdf2-possible-infinite-loop-when-a-comment-isn-t)
- [PYSEC-2026-1836 - PyPDF2 vulnerable to possible Infinite Loop when reading malformed objects](https://junglewise.ai/threats/cve-2023-36807-pypdf2-vulnerable-to-possible-infinite-loop-when-reading)
- [Manipulated inline images can cause Infinite Loop in PyPDF2](https://junglewise.ai/threats/cve-2022-24859-manipulated-inline-images-can-cause-infinite-loop-in-pypdf2)