How severe is CVE-2026-84309?

No CVSS score has been assigned to CVE-2026-84309 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-84309?

CVE-2026-84309 affects the following packages: pypdf (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-84309?

Update pypdf to 6.16.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84309 is resolved across your whole dependency graph.

How do I detect CVE-2026-84309 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pypdf, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-84309 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-84309 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-84309 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-84309?

CVE-2026-84309 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 8th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-84309?

CVE-2026-84309 is classified as CWE-835 (CWE-835). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-84309 published, and has it been updated?

CVE-2026-84309 was published on September 1, 2026 and was last updated on October 7, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2026-84309 — pypdf

Fix: py-pdf/pypdf@c9ba557

CVE-2026-84309 is a CWE-835 vulnerability in pypdf. A fix is available for pypdf — see the affected versions and patch details below.

pypdf: Possible infinite loop for TreeObject.insert_child

Also known asGHSA-jp53-mhqp-8xcgPYSEC-2026-3913

Published

Sep 1, 2026

Updated

Oct 7, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 16, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-84309.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk+0.01%

Lower risk than most CVEs8th percentile — riskier than 8% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍pypdf

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Impact

An attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This requires a (usually writing) code path where TreeObject.insert_child is involved.

Patches

This has been fixed in pypdf==6.16.0.

Workarounds

If you cannot upgrade yet, consider applying the changes from PR #3964.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`pypdf`	all versions	6.16.0`pip install --upgrade 'pypdf==6.16.0'`

Affected Products

1 product · 1 configurations

Application

pypdfpypdf_project

< 6.16.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pypdf, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update pypdf to 6.16.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84309 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Impact An attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This requires a (usually writing) code path where `TreeObject.insert_child` is involved. ### Patches This has been fixed in [pypdf==6.16.0](https://github.com/py-pdf/pypdf/releases/tag/6.16.0). ### Workarounds If you cannot upgrade yet, consider applying the changes from PR [#3964](https://github.com/py-pdf/pypdf/pull/3964).

O3 Security · Impact-Aware SCA

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