HighVulnerabilityCVE-2026-119209updated 30 Oct 2026, 23:08 UTC

pypdf can use excessive memory when opening a crafted PDF

A specially crafted PDF file can make the pypdf Python library use up huge amounts of memory and slow or crash the program that opens it. Opening an untrusted PDF is the main risk.

Fixed in pypdf 6.21.3 · out 2026-10-30 23:08 UTCOfficial, 2 sources

Severity	HighCVSS 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

1Attacker crafts PDFAdds cross-reference streams with huge entry counts
2PDF is deliveredUploaded or sent to a service
3pypdf opens fileParses the malicious cross-reference data
4Memory exhaustedParsed entries multiply across the document
ResultService slows down or crashes

What happened

pypdf versions before 6.21.3 consume excessive memory when parsing PDFs with cross-reference streams that declare very large entry counts, because compressible streams and /Prev chains multiply parsed entries and negative /Index counts bypass the existing clamp.

Why it is dangerous: A malicious PDF can exhaust memory on the machine processing it, causing denial of service. Services that accept and parse PDFs from users or the internet are most at risk.

Are you affected?

You are affected if you use pypdf older than 6.21.3 to open PDF files that may come from untrusted sources.

Package / product	Affected versions	Fixed in
pypdf · pip	< 6.21.3	6.21.3

What to do

Update pypdf to version 6.21.3 or later (pip install --upgrade pypdf)
If you cannot upgrade yet, apply the changes from PR #4269 in the pypdf repository
Limit memory for processes that open untrusted PDFs until patched

Timeline

29 Oct 2026, 21:17 UTC
Publicly disclosed
29 Oct 2026, 21:17 UTC
Reported by NVD · NVD
29 Oct 2026, 21:21 UTC
Picked up by Zero Radar
30 Oct 2026, 23:08 UTC
GitHub Advisory reported on it · GitHub Advisory
30 Oct 2026, 23:08 UTC
Fixed version published: pypdf 6.21.3 · GitHub Advisory

Sources 2 reports, oldest first

Official vendor, government CERT or advisory database

CVE-2026-119209NVD · 29 Oct 2026, 21:17 UTC
pypdf has possible large memory usage when parsing cross-reference streamsGitHub Advisory · 30 Oct 2026, 23:07 UTC

Technical details

ID: CVE-2026-119209 · GHSA-x3rh-gjgm-fmqc
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, 23:08 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