GitHub Advisoryadvisory · PyPI
GHSA-m449-cwjh-6pw7 pypdf's LZWDecode streams be manipulated to exhaust RAM
MEDIUM
Official page ↗
- Aliases
- CVE-2025-66019
- Ecosystem
- PyPI
- Packages
- pypdf
- Severity
- Moderate
- CVSS vector
- CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U
- Weaknesses
- CWE-400, CWE-409
- Reviewed
- 2025-11-24
Affected packages
• PyPI pypdf: < 6.4.0 → fixed in 6.4.0
Description
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 to align the default limit with the one for *zlib*.
Patches
This has been fixed in pypdf==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
```
Related
Alias · CVE (1)
- CVE-2025-66019 pypdf is a free and open-source pure-python PDF library. vulnerability
References
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-jfx9-29x2-rv3j web
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-m449-cwjh-6pw7 web
- https://nvd.nist.gov/vuln/detail/CVE-2025-66019 advisory
- https://github.com/py-pdf/pypdf/commit/96186725e5e6f237129a58a97cd19204a9ce40b2 web
- https://aydinnyunus.github.io/2025/12/20/cve-2025-66019-pypdf-lzw-dos web
- https://github.com/py-pdf/pypdf package
- https://github.com/py-pdf/pypdf/releases/tag/6.4.0 web