pypdf is a free and open-source pure-python PDF library. Prior to 6.21.3, pypdf can consume excessive memory while opening a crafted PDF containing cross-reference streams that declare very large entry counts. Highly compressible streams and /Prev chains can multiply the number of parsed entries across a document, while negative /Index counts can bypass the existing per-stream clamp. This issue is fixed in version 6.21.3.
CVE-2026-119209
CVSS base score
5.5 (v3.1)
Severity
MEDIUM
Attack vector
Local
Weakness
CWE-400, CWE-770
Last modified
November 2, 2026
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Affected products
py-pdf pypdf
References
- github.com Patch
- github.com Patch
- github.com Release Notes
- github.com Patch, Vendor Advisory