CVE-2026-54651 pypdf: Possible infinite loop when processing threads/articles in writer
An attacker can cause an infinite loop in pypdf by crafting a PDF with threads or articles during a merge operation, leading to denial of service.
- 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-2026-54651?
CVE-2026-54651 is a medium-severity denial of service vulnerability in Pypdf Project Pypdf, published on 22 Jun 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. Prior to 6.13.1, an attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This requires merging a file with threads/articles into a writer. This vulnerability is fixed in 6.13.1.
Weakness: CWE-835
Which versions are affected by CVE-2026-54651?
3 open source packages ship an affected version, including pypdf. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pypdf PyPI | All versions | 6.13.1 |
pypdf PyPI | All versions | 6.13.1 |
pypdf PyPI | All versions | 6.13.1 |
Linux distribution packages (1)
python-pypdf openSUSE:Tumbleweed | All versions | 6.14.0-1.1 |
Products include Pypdf Project Pypdf.
How do I fix CVE-2026-54651?
Upgrade pypdf to 6.13.1 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-2026-54651 being exploited?
There is no known exploitation of CVE-2026-54651 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 CLEANSTART-2026-PT72427, CLSA-2026-1784077473, DEBIAN-CVE-2026-54651, ECHO-fb4e-0a86-0a3c, GHSA-g9xf-7f8q-9mcj, MINI-27mr-88c6-mxx6 and 10 more.