---
id: CVE-2025-66019
aliases:
  - GHSA-m449-cwjh-6pw7
  - PYSEC-2026-1832
title: pypdf's LZWDecode streams be manipulated to exhaust RAM
summary: pypdf's LZWDecode streams be manipulated to exhaust RAM
severity: medium
vendor: pypdf
product: pypdf
ecosystem: pip
affected:
  - pypdf < 6.4.0
patched:
  - pypdf 6.4.0
published: '2025-11-24'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:31.107367078Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-m449-cwjh-6pw7'
references:
  - url: 'https://github.com/py-pdf/pypdf/security/advisories/GHSA-jfx9-29x2-rv3j'
  - url: 'https://github.com/py-pdf/pypdf/security/advisories/GHSA-m449-cwjh-6pw7'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-66019'
  - url: >-
      https://github.com/py-pdf/pypdf/commit/96186725e5e6f237129a58a97cd19204a9ce40b2
  - url: 'https://aydinnyunus.github.io/2025/12/20/cve-2025-66019-pypdf-lzw-dos'
  - url: 'https://github.com/py-pdf/pypdf'
  - url: 'https://github.com/py-pdf/pypdf/releases/tag/6.4.0'
tags:
  - osv
  - pip
epss: 0.00361
epssPercentile: 0.29955
ingestedAt: '2026-07-08T18:25:51.119Z'
---

## Overview

### Impact

An attacker who uses this vulnerability can craft a PDF which leads to a memory usage of up to 1 GB per stream. This requires parsing the content stream of a page using the LZWDecode filter.

This is a follow up to [GHSA-jfx9-29x2-rv3j](https://github.com/py-pdf/pypdf/security/advisories/GHSA-jfx9-29x2-rv3j) to align the default limit with the one for *zlib*.

### Patches
This has been fixed in [pypdf==6.4.0](https://github.com/py-pdf/pypdf/releases/tag/6.4.0).

### Workarounds
If users cannot upgrade yet, use the line below to overwrite the default in their code:

```python
pypdf.filters.LZW_MAX_OUTPUT_LENGTH = 75_000_000
```

## Affected packages

- `pypdf < 6.4.0`

## Remediation

Upgrade to a patched release:

- `pypdf 6.4.0`