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HighVulnerabilityCVE-2026-119206updated 30 Oct 2026, 23:09 UTC

pypdf can hang on crafted PDFs when reading page labels

A specially crafted PDF file can make the pypdf Python library run extremely slowly when it reads page labels. This can tie up a program or server for a long time.

Fixed in pypdf 6.21.3 · out Official, 2 sources
SeverityHighCVSS 7.1 of 10
Being exploited?UnclearNo reports either way yet
Fix available?Yespypdf 6.21.3 · since 30 Oct 2026
How sure is this?Official, 2 sourcesBacked by an official source

How the attack works simplified

  1. 1Crafted PDFMany label ranges in the page-label tree
  2. 2App reads labelsProgram calls page_labels on the file
  3. 3Repeated scansSame array rescanned for every page
  4. 4Slow processingRuntime grows with pages times ranges
  5. ResultProgram or server becomes unresponsive

What happened

In pypdf before 6.21.3, the page_labels property re-scans the same /Nums array from the start for every page, so work grows with both page count and number of label ranges. A crafted PDF with many label ranges causes excessive runtime.

Why it is dangerous: Applications that parse untrusted PDFs, such as upload or document-processing services, can be slowed down or made unresponsive (denial of service).

Are you affected?

You are affected if you use the pypdf Python package before version 6.21.3 and read page labels from PDF files, especially files you do not fully trust.

Package / productAffected versionsFixed in
pypdf · pip< 6.21.36.21.3

What to do

  1. Upgrade pypdf to version 6.21.3 or later (pip install --upgrade pypdf)
  2. If you cannot upgrade yet, apply the changes from PR #4251 in the pypdf repository
  3. Be cautious when reading page labels from PDFs you did not create

Timeline

  1. 29 Oct 2026, 21:17 UTC
    Publicly disclosed
  2. 29 Oct 2026, 21:17 UTC
    Reported by NVD · NVD
  3. 29 Oct 2026, 21:21 UTC
    Picked up by Zero Radar
  4. 30 Oct 2026, 23:09 UTC
    GitHub Advisory reported on it · GitHub Advisory
  5. 30 Oct 2026, 23:09 UTC
    Fixed version published: pypdf 6.21.3 · GitHub Advisory

Sources 2 reports, oldest first

Official vendor, government CERT or advisory database

Technical details

ID
CVE-2026-119206 · GHSA-42gh-23hr-vphw
CVSS
7.1 / 10
Disclosed
29 Oct 2026, 21:17 UTC
On Zero Radar
29 Oct 2026, 21:21 UTC (4 min after disclosure)
Last change
30 Oct 2026, 23:09 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

pypdf can hang on crafted PDFs when reading page labels · Zero Radar