# CVE-2026-119203: pypdf infinite loop in PDF cross-reference parsing

Source: https://junglewise.ai/threats/cve-2026-119203-pypdf-is-a-free-and-open-source-pure-python-pdf-library-prior-to  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-29. Updated: 2026-10-29  
License: CC BY 4.0 with a link back

CVE-2026-119203 · Severity: high · CVSS 4 · Published 2026-10-29

pypdf is a Python library for reading and writing PDF files. A maliciously crafted incomplete PDF can cause pypdf to enter an infinite loop when parsing the file's cross-reference table, blocking the application thread and preventing further processing. This results in a denial-of-service condition for any application using the library to process untrusted PDFs.

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

## Quick answers

**Is CVE-2026-119203 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-119203 being exploited in the wild.

**How severe is CVE-2026-119203?** High severity, with a CVSS score of 4, published 29 October 2026.

**Which products and versions are affected?** Pypdf before 6.21.4; pypdf (PyPI) < 6.21.4, ECOSYSTEM:introduced=0,fixed=6.21.4.

**Is there a fix for CVE-2026-119203?** Yes. pypdf (PyPI): upgrade to 6.21.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-119203 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-119203?** Check whether you run 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 6.21.4 or later

  ```sh
  pip install "pypdf>=6.21.4"
  ```


## Technical details

The vulnerability exists in the standard cross-reference table parsing routine (_read_standard_xref_table). When a malformed PDF's xref table reaches end-of-file without a proper trailer keyword, the parser can rewind to the same stream position repeatedly instead of terminating, causing an infinite loop. The fix detects when the parser rewinds to a previously seen position and raises an exception, preventing the denial-of-service.

## Affected products

- pypdf pypdf before 6.21.4

## Identifiers

- CVE-2026-119203
- GHSA-5849-834g-hvw5

## Timeline

- 2026-10-28: patched: Fix merged in PR #4289
- 2026-10-29: advisory

## References

- [https://github.com/py-pdf/pypdf/commit/06593f993789a4b573dd955730c1a7051128bb2a](https://github.com/py-pdf/pypdf/commit/06593f993789a4b573dd955730c1a7051128bb2a)
- [https://github.com/py-pdf/pypdf/pull/4289](https://github.com/py-pdf/pypdf/pull/4289)

## 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)