# CVE-2026-102998: pypdf denial of service in appearance stream generation

Source: https://junglewise.ai/threats/cve-2026-102998-pypdf-is-a-free-and-open-source-pure-python-pdf-library-prior-to  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-30. Updated: 2026-09-30  
License: CC BY 4.0 with a link back

CVE-2026-102998 · Severity: high · CVSS 4 · Published 2026-09-30

pypdf is a Python library for reading and modifying PDF files. A specially crafted PDF with form fields can cause the library to perform excessive repeated computations when updating fields with flattening enabled, leading to application slowdowns or unavailability. The issue affects versions prior to 6.19.0 and is resolved in that release.

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-2026-102998 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-102998 being exploited in the wild.

**How severe is CVE-2026-102998?** High severity, with a CVSS score of 4, published 30 September 2026.

**Which products and versions are affected?** Py-Pdf Pypdf before 6.19.0; pypdf (PyPI) < 6.19.0, ECOSYSTEM:introduced=0,fixed=6.19.0.

**Is there a fix for CVE-2026-102998?** Yes. pypdf (PyPI): upgrade to 6.19.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-102998 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-102998?** 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 6.19.0 or later

  ```sh
  pip install "pypdf>=6.19.0"
  ```


## Technical details

The vulnerability exists in pypdf/generic/_appearance_stream.py where invariant selection-data work is repeated inside a loop during appearance stream generation for form field updates with flattening enabled. An attacker can provide a maliciously crafted PDF to trigger this inefficiency. The fix involves moving static computations outside the loop body to avoid redundant processing.

## Affected products

- py-pdf pypdf before 6.19.0

## Identifiers

- CVE-2026-102998
- GHSA-php9-fj8v-98fj
- PYSEC-2026-4157

## Timeline

- 2026-09-16: patched
- 2026-09-30: disclosed

## References

- [https://github.com/py-pdf/pypdf/commit/959467a9b95be83e2dc5ae873ece5f371263ede7](https://github.com/py-pdf/pypdf/commit/959467a9b95be83e2dc5ae873ece5f371263ede7)
- [https://github.com/py-pdf/pypdf/pull/4087](https://github.com/py-pdf/pypdf/pull/4087)

## 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)