CVE-2026-84310: pypdf Possible Long Runtimes/large Memory Usage Vulnerability

MODERATE
Advisory Identifier: GHSA-23w6-3w8w-8484
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CWE-405 CWE-834
Published
Advisory Summary

CVE-2026-84310 is a MODERATE possible long runtimes/large memory usage vulnerability (CWE-405: Asymmetric Resource Consumption (Amplification)) affecting pypdf libraries in the PyPI ecosystem. The issue involves possible long runtimes/large memory usage when retrieving outlines. Remediation is available by upgrading affected packages to version 6.16.1.

CVE-2026-84310 at a Glance

CVE Identifier CVE-2026-84310
GHSA Identifier GHSA-23w6-3w8w-8484
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-405: Asymmetric Resource Consumption (Amplification)
Affected Product pypdf
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix CVE-2026-84310

To remediate this vulnerability, upgrade all affected pypdf dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

pypdf fixed: 6.16.1 
pip install pypdf>=6.16.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show pypdf

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-84310, inspect your installed packages using pip:

pip show pypdf

Analyze the terminal output to locate any version of pypdf in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.16.1), your application is affected.

Note: The pip show pypdf command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-405: Asymmetric Resource Consumption (Amplification), where the product does not properly control situations in which an adversary can cause the product to consume or produce excessive resources without requiring the adversary to invest equivalent work or otherwise prove authorization, i.e., the adversary's influence is "asymmetric.". In pypdf, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact An attacker who uses this vulnerability can craft a PDF which leads to long runtimes and large memory consumption. This requires accessing the outlines of a document with either lots of entries or nested outlines with long re-used nesting paths. ### Patches This has been fixed in [pypdf==6.16.1](https://github.com/py-pdf/pypdf/releases/tag/6.16.1). ### Workarounds If you cannot upgrade yet, consider applying the changes from PR [#3966](https://github.com/py-pdf/pypdf/pull/3966).

CVE-2026-84310 Affected pypdf Versions

1 component(s)
Fixed Versions:
6.16.1
Product / Package Ecosystem Affected Versions Fixed Version
pypdf
pypi/pypdf
PyPI
< 6.16.1
6.16.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/py-pdf/pypdf/security/advisories/GHSA-23w6-3w8w-8484
pypdf Source Repository REPOSITORY
https://github.com/py-pdf/pypdf/pull/3966
Security Fix Commit FIX COMMIT
https://github.com/py-pdf/pypdf/commit/d91ab705fd81ed1a9cec175c6958600dea1a4942
pypdf Source Repository REPOSITORY
https://github.com/py-pdf/pypdf
pypdf Release RELEASE
https://github.com/py-pdf/pypdf/releases/tag/6.16.1

Frequently Asked Questions

What is CVE-2026-84310?
CVE-2026-84310 is a security vulnerability in pypdf involving Possible long runtimes/large memory usage when retrieving outlines under CWE-405: Asymmetric Resource Consumption (Amplification).
Which pypdf versions are affected?
Affected versions include releases prior to 6.16.1 across affected packages: pypdf.
What version fixes CVE-2026-84310?
Upgrading to 6.16.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pypdf affected?
Yes, pypdf is affected in releases prior to 6.16.1. Upgrade your dependency to 6.16.1 or later.
What CWE is associated with CVE-2026-84310?
CVE-2026-84310 is classified under CWE-405: Asymmetric Resource Consumption (Amplification) (The product does not properly control situations in which an adversary can cause the product to consume or produce excessive resources without requiring the adversary to invest equivalent work or otherwise prove authorization, i.e., the adversary's influence is "asymmetric.").
How can I check PyPI dependencies for CVE-2026-84310?
Run the dependency tree command: 'pip show pypdf'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-23w6-3w8w-8484",
  "modified" : "2026-09-01T21:28:38Z",
  "published" : "2026-09-01T21:28:37Z",
  "aliases" : [ "CVE-2026-84310" ],
  "summary" : "pypdf: Possible long runtimes/large memory usage when retrieving outlines",
  "details" : "### Impact\n\nAn attacker who uses this vulnerability can craft a PDF which leads to long runtimes and large memory consumption. This requires accessing the outlines of a document with either lots of entries or nested outlines with long re-used nesting paths.\n\n### Patches\n\nThis has been fixed in [pypdf==6.16.1](https://github.com/py-pdf/pypdf/releases/tag/6.16.1).\n\n### Workarounds\n\nIf you cannot upgrade yet, consider applying the changes from PR [#3966](https://github.com/py-pdf/pypdf/pull/3966).",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pypdf"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.16.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/py-pdf/pypdf/security/advisories/GHSA-23w6-3w8w-8484"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/py-pdf/pypdf/pull/3966"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/py-pdf/pypdf/commit/d91ab705fd81ed1a9cec175c6958600dea1a4942"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/py-pdf/pypdf"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/py-pdf/pypdf/releases/tag/6.16.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-405", "CWE-834" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-01T21:28:37Z",
    "nvd_published_at" : null
  }
}