GHSA-m449-cwjh-6pw7
pypdf's LZWDecode streams be manipulated to exhaust RAM
Packages
Details
As written in the advisory (Markdown source, shown as plain text).
### Impact
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 is a follow up to [GHSA-jfx9-29x2-rv3j](https://github.com/py-pdf/pypdf/security/advisories/GHSA-jfx9-29x2-rv3j) to align the default limit with the one for *zlib*.
### Patches
This has been fixed in [pypdf==6.4.0](https://github.com/py-pdf/pypdf/releases/tag/6.4.0).
### Workarounds
If users cannot upgrade yet, use the line below to overwrite the default in their code:
```python
pypdf.filters.LZW_MAX_OUTPUT_LENGTH = 75_000_000
```
References
External links from the advisory. They lead to third-party sites.
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-jfx9-29x2-rv3j
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-m449-cwjh-6pw7
- https://nvd.nist.gov/vuln/detail/CVE-2025-66019
- https://github.com/py-pdf/pypdf/commit/96186725e5e6f237129a58a97cd19204a9ce40b2
- https://aydinnyunus.github.io/2025/12/20/cve-2025-66019-pypdf-lzw-dos
- https://github.com/py-pdf/pypdf
- https://github.com/py-pdf/pypdf/releases/tag/6.4.0