CVE-2026-33123 pypdf has inefficient decoding of array-based streams
An attacker can cause denial of service via long runtimes or high memory usage by crafting a malicious PDF with array-based streams in pypdf.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33123?
CVE-2026-33123 is a medium-severity denial of service vulnerability in Pypdf Project Pypdf, published on 20 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
pypdf is a free and open-source pure-python PDF library. Versions prior to 6.9.1 allow an attacker to craft a malicious PDF which leads to long runtimes and/or large memory usage. Exploitation requires accessing an array-based stream with many entries. This issue has been fixed in version 6.9.1.
Which versions are affected by CVE-2026-33123?
3 open source packages ship an affected version, including pypdf. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pypdf PyPI | All versions | 6.9.1 |
pypdf PyPI | All versions | 6.9.1 |
pypdf PyPI | All versions | 6.9.1 |
Linux distribution packages (2)
python-PyPDF2 openSUSE:Tumbleweed | All versions | 2.11.1-8.1 |
python-pypdf openSUSE:Tumbleweed | All versions | 6.9.1-1.1 |
Products include Pypdf Project Pypdf.
How do I fix CVE-2026-33123?
Upgrade pypdf to 6.9.1 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-33123 being exploited?
There is no known exploitation of CVE-2026-33123 in the wild and no public exploit code.
Other vulnerabilities in Pypdf Project Pypdf
- CVE-2026-102993 pypdf: Possible large memory usage when retrieving Roman page labels
- CVE-2026-102994 pypdf: Possible long runtimes/large memory usage when parsing indirect objects
- CVE-2026-102995 pypdf: Possible large memory usage for large /ToUnicode streams (Follow-up 2)
- CVE-2026-102996 pypdf: Possible large memory usage when parsing font data
- CVE-2026-102997 pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)
Sources
Also known as DEBIAN-CVE-2026-33123, ECHO-bc03-0ce7-e396, GHSA-qpxp-75px-xjcp, MINI-3rvm-v6j7-4gg8, MINI-8wcx-vfpq-5j84, PYSEC-2026-3023 and 4 more.