# CVE-2026-27628: PYSEC-2026-3005 - pypdf has a possible infinite loop when loading circular /Prev entries in cross-reference streams

Source: https://junglewise.ai/threats/cve-2026-27628-pypdf-infinite-loop-in-circular-cross-reference-streams  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-02-25. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-27628 · Severity: high · CVSS 7.5 · Published 2026-02-25

pypdf is a popular Python library for reading and manipulating PDF files. A vulnerability allows an attacker to craft a malicious PDF that causes an infinite loop when the library attempts to load cross-reference data, potentially leading to a denial of service that consumes CPU resources and halts PDF processing.

Technologies: [Py-Pdf Pypdf](https://junglewise.ai/threats/technologies/py-pdf-pypdf), [pypdf (PyPI)](https://junglewise.ai/threats/technologies/pypdf). Vendors: [Py-Pdf](https://junglewise.ai/threats/vendors/py-pdf), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-27628 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-27628 being exploited in the wild.

**How severe is CVE-2026-27628?** High severity, with a CVSS score of 7.5, published 25 February 2026.

**Which products and versions are affected?** pypdf (PyPI) ECOSYSTEM:introduced=0,fixed=6.7.2.

**Is there a fix for CVE-2026-27628?** Yes. pypdf (PyPI): upgrade to 6.7.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-27628 attacked?** It is attacked over the network or with local access, in a software library.

**Am I affected by CVE-2026-27628?** Check whether you run Py-Pdf Pypdf or 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 6.7.2 or later

  ```sh
  pip install "pypdf>=6.7.2"
  ```


## Technical details

The vulnerability is a classic infinite loop (CWE-835) triggered by circular /Prev entries in PDF cross-reference streams. When pypdf parses a PDF file, it follows the /Prev chain in the xref stream to reconstruct document history; a circular reference causes this chain-following logic to loop indefinitely. The attack vector is network/local file access: an attacker must craft a malicious PDF and trick a user or system into opening it. The vulnerability affects all versions prior to 6.7.2 and has been patched in that release.

## Affected products

- py-pdf pypdf before 6.7.2

## Identifiers

- CVE-2026-27628
- GHSA-2rw7-x74f-jg35
- PYSEC-2026-3005

## Timeline

- 2026-02-22: disclosed: Advisory published on GitHub
- 2026-02-25: patched: Fix released in pypdf 6.7.2

## References

- [https://github.com/py-pdf/pypdf/security/advisories/GHSA-2rw7-x74f-jg35](https://github.com/py-pdf/pypdf/security/advisories/GHSA-2rw7-x74f-jg35)

## 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)