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MEDIUM severity

PyPDF2 quadratic runtime with malformed PDF missing xref markerGHSA-jrm6-h9cq-8gqw

MEDIUMFix: py-pdf/pypdf#808

GHSA-jrm6-h9cq-8gqw is a medium-severity (CVSS 6.2) CWE-407 vulnerability in pypdf2. 2 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for pypdf2 — see the affected versions and patch details below.

Also known asCVE-2023-36810PYSEC-2026-1837
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
2 known
Exploitation data as of Nov 4, 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 GHSA-jrm6-h9cq-8gqw.

EPSS Exploitation Probability

via FIRST.org ↗
0.6%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs50th percentile — riskier than 50% of all scored CVEsHighest risk
0.00%0.38%0.75%1.13%0.2%0.6%May 26Sep 26Nov 26

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐍pypdf2

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 unexpected long runtime. This quadratic runtime blocks the current process and can utilize a single core of the CPU by 100%. It does not affect memory usage.

Patches

https://github.com/py-pdf/pypdf/pull/808

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading?

References

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIpypdf2all versions1.27.9pip install --upgrade 'pypdf2==1.27.9'

Affected Products

1 product · 1 configurations
Application
pypdfpy-pdf
≤ 1.27.8
range
Exploits & PoCs
2

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

pypdf is a pure-python PDF library capable of splitting, merging, croppi…

github.comNVDJul 2023

Report on github.com

github.comNVDJul 2023

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pypdf2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update pypdf2 to 1.27.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-jrm6-h9cq-8gqw is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Impact An attacker who uses this vulnerability can craft a PDF which leads to unexpected long runtime. This quadratic runtime blocks the current process and can utilize a single core of the CPU by 100%. It does not affect memory usage. ### Patches https://github.com/py-pdf/pypdf/pull/808 ### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ ### References * [PyPDF2 PR #808](https://github.com/py-pdf/pypdf/pull/808) * [PyPDF2 Issue #582](https://github.com/py-pdf/pypdf/issues/582)
O3 Security · Impact-Aware SCA

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PyPDF2 quadratic runtime with malformed PDF missing…