CVE-2025-66019 pypdf manipulated LZWDecode streams can exhaust RAM
Attackers can cause excessive memory consumption and potential service disruption by crafting malicious PDFs with LZWDecode streams in pypdf.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-66019?
CVE-2025-66019 is a medium-severity denial of service vulnerability in py-pdf pypdf, published on 25 Nov 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
pypdf is a free and open-source pure-python PDF library. Prior to version 6.4.0, an attacker who uses this vulnerability can craft a PDF which leads to a memory usage of up to 1 GB per stream. This requires parsing the content stream of a page using the LZWDecode filter. This issue has been patched in version 6.4.0.
Which versions are affected by CVE-2025-66019?
3 open source packages ship an affected version, including pypdf.
| Package | Affected | Fixed in |
|---|---|---|
pypdf PyPI | All versions | 6.4.0 |
pypdf PyPI | All versions | 6.4.0 |
pypdf PyPI | All versions | 6.4.0 |
Linux distribution packages (1)
python-pypdf openSUSE:Tumbleweed | All versions | 6.4.0-1.1 |
How do I fix CVE-2025-66019?
Upgrade pypdf to 6.4.0 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-2025-66019 being exploited?
There is no known exploitation of CVE-2025-66019 in the wild and no public exploit code.
Sources
Also known as GHSA-m449-cwjh-6pw7, PYSEC-2026-1832, UBUNTU-CVE-2025-66019, openSUSE-SU-2025:15776-1.