pypdf's LZWDecode streams be manipulated to exhaust RAM
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:
pypdf.filters.LZW_MAX_OUTPUT_LENGTH = 75_000_000Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pypdf | < 6.4.0 | 6.4.0 |
References
- 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
- https://pypi.org/project/pypdf
- https://github.com/advisories/GHSA-m449-cwjh-6pw7
- 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- Weakness (CWE)
CWE-400, CWE-409- Platform
- Python (PyPI)
- Package
pypdf- Disclosed
- 24.11.2025
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1832 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-m449-cwjh-6pw7 - CC BY 4.0
Vulnerability history: pypdf
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 51
- First → latest
- 06.2023 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 10
- Medium 38
- Low 3
Disclosures per year
- 2023: 2
- 2024: 0
- 2025: 4
- 2026: 45
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pypdf's LZWDecode streams be manipulated to exhaust RAM this entry
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