CVE-2026-48156 pypdf: Possible long runtimes for zero-only width values in cross-reference streams
An attacker can cause excessive CPU consumption and long runtimes by crafting a PDF with specific cross-reference stream values, affecting applications using the pypdf library.
- 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-2026-48156?
CVE-2026-48156 is a medium-severity denial of service vulnerability in Pypdf Project Pypdf, published on 28 May 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 6.12.0, an attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires cross-reference streams with /W [0 0 0] values and large /Size values. This vulnerability is fixed in 6.12.0.
Weakness: CWE-834
Which versions are affected by CVE-2026-48156?
3 open source packages ship an affected version, including pypdf. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pypdf PyPI | All versions | 6.12.0 |
pypdf PyPI | All versions | 6.12.0 |
pypdf PyPI | All versions | 6.12.0 |
Products include Pypdf Project Pypdf.
How do I fix CVE-2026-48156?
Upgrade pypdf to 6.12.0 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-2026-48156 being exploited?
There is no known exploitation of CVE-2026-48156 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-CS26943, DEBIAN-CVE-2026-48156, ECHO-2495-c2a6-88b6, GHSA-248m-82v9-q6g6, MINI-4wgq-r84q-6xf2, MINI-5hv5-9w6g-x6w8 and 7 more.