---
id: CVE-2026-27026
aliases:
  - GHSA-9mvc-8737-8j8h
  - PYSEC-2026-3015
title: pypdf possibly has long runtimes for malformed FlateDecode streams
summary: pypdf possibly has long runtimes for malformed FlateDecode streams
severity: medium
vendor: pypdf
product: pypdf
ecosystem: pip
affected:
  - pypdf < 6.7.1
patched:
  - pypdf 6.7.1
published: '2026-02-18'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:50:34.680998937Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-9mvc-8737-8j8h'
references:
  - url: 'https://github.com/py-pdf/pypdf/security/advisories/GHSA-9mvc-8737-8j8h'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-27026'
  - url: 'https://github.com/py-pdf/pypdf/pull/3644'
  - url: >-
      https://github.com/py-pdf/pypdf/commit/7905842d833f899f1d3228af7e7467ad80277016
  - url: 'https://github.com/py-pdf/pypdf'
  - url: 'https://github.com/py-pdf/pypdf/releases/tag/6.7.1'
tags:
  - osv
  - pip
epss: 0.00184
epssPercentile: 0.07105
ingestedAt: '2026-07-13T18:57:56.017Z'
---

## Overview

### Impact

An attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires a malformed `/FlateDecode` stream, where the byte-by-byte decompression is used.

### Patches

This has been fixed in [pypdf==6.7.1](https://github.com/py-pdf/pypdf/releases/tag/6.7.1).

### Workarounds

If you cannot upgrade yet, consider applying the changes from PR [#3644](https://github.com/py-pdf/pypdf/pull/3644).

## Affected packages

- `pypdf < 6.7.1`

## Remediation

Upgrade to a patched release:

- `pypdf 6.7.1`