What is CVE-2026-82398?

CVE-2026-82398 is a medium-severity vulnerability in Py-Pdf Pypdf, classified under Inefficient Algorithmic Complexity. CVSS score: 5.3/10. Published 2026-08-31.

How severe is CVE-2026-82398?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Py-Pdf Pypdf

CVE-2026-82398

pypdf is a free and open-source pure-python PDF library. Prior to 6.15.0, an attacker can craft a PDF that causes long runtimes when the pypdf/_utils.py function read_until_whitespace reads a stream containing a long run of bytes without whitespace. The function repeatedly performs immutable bytes concatenation in a one-byte loop, causing quadratic processing cost for the long non-whitespace input. This issue is fixed in version 6.15.0.

Published 2026-08-31 · last modified 2026-10-05.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.005 (43.1th percentile), scored 2026-10-16.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 43.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002

Affected products

Py-Pdf Pypdf — versions < 6.15.0
Pypdf Project

Weakness classification (CWE)

CWE-407 — Inefficient Algorithmic Complexity

References

github.com/py-pdf/pypdf/security/advisories/GHSA-fc8x-2rww-xw9m (Patch, Vendor Advisory)
github.com/py-pdf/pypdf/pull/3947 (Patch)
github.com/py-pdf/pypdf/commit/4959848e057e37c218dccad7465259210923faaa (Patch)
github.com/py-pdf/pypdf/releases/tag/6.15.0 (Release Notes)

Frequently asked questions

What is CVE-2026-82398?: CVE-2026-82398 is a medium-severity vulnerability in Py-Pdf Pypdf, classified under Inefficient Algorithmic Complexity. CVSS score: 5.3/10. Published 2026-08-31.
How severe is CVE-2026-82398?: Medium severity. CVSS v3 base score is 5.3 out of 10.