Medium 6.6Published Nov 25, 2025

CVE-2025-66019pypdf manipulated LZWDecode streams can exhaust RAM

Updated under an hour ago (Oct 26, 2026, 10:50 AM ET)

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Every CVE for py-pdf pypdf

Exploited in the last 30 days

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.

CVSS: 6.6 MEDIUM (v4.0, CNA)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
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Jan 20, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

py-pdf pypdf py_pdf:pypdf (from the name)	before 6.4.0	CNA record

References

https://github.com/py-pdf/pypdf/security/advisories/GHSA-m449-cwjh-6pw7x-refsource-confirm
https://github.com/py-pdf/pypdf/commit/96186725e5e6f237129a58a97cd19204a9ce40b2x-refsource-misc
https://github.com/py-pdf/pypdf/releases/tag/6.4.0x-refsource-misc
https://aydinnyunus.github.io/2025/12/20/cve-2025-66019-pypdf-lzw-dos/

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.