What is CVE-2026-84309?

CVE-2026-84309 is a medium-severity vulnerability in Py-Pdf Pypdf, classified under Loop with Unreachable Exit Condition (Infinite Loop). CVSS score: 5.5/10. Published 2026-09-01.

How severe is CVE-2026-84309?

Medium severity. CVSS v3 base score is 5.5 out of 10.

Vulnerability in Py-Pdf Pypdf

CVE-2026-84309

pypdf is a free and open-source pure-python PDF library. Prior to 6.16.0, an attacker can craft a PDF whose cyclic tree structure causes pypdf/generic/_data_structures.py TreeObject.insert_child to follow /Next links indefinitely when a writing code path inserts a child, producing an infinite loop. This issue is fixed in version 6.16.0.

Published 2026-09-01 · last modified 2026-10-05.

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.002 (7.7th percentile), scored 2026-10-17.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 8th percentile — 7.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.001

Affected products

Py-Pdf Pypdf — versions < 6.16.0
Pypdf Project

Weakness classification (CWE)

CWE-835 — Loop with Unreachable Exit Condition (Infinite Loop)

References

github.com/py-pdf/pypdf/security/advisories/GHSA-jp53-mhqp-8xcg (Patch, Vendor Advisory)
github.com/py-pdf/pypdf/pull/3964 (Patch)
github.com/py-pdf/pypdf/commit/c9ba557d565d57c53a0b3a0be06c0a4c29b0559b (Patch)
github.com/py-pdf/pypdf/releases/tag/6.16.0 (Release Notes)

Frequently asked questions

What is CVE-2026-84309?: CVE-2026-84309 is a medium-severity vulnerability in Py-Pdf Pypdf, classified under Loop with Unreachable Exit Condition (Infinite Loop). CVSS score: 5.5/10. Published 2026-09-01.
How severe is CVE-2026-84309?: Medium severity. CVSS v3 base score is 5.5 out of 10.