CVE-2026-48156: pypdf Possible Long Runtimes For Zero-only Vulnerability

MODERATE
Advisory Identifier: GHSA-248m-82v9-q6g6
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CVSS 3.3
CWE-834
Published
Advisory Summary

CVE-2026-48156 is a MODERATE (CVSS 3.3) possible long runtimes for zero-only vulnerability (CWE-834: Excessive Iteration) affecting pypdf libraries in the PyPI ecosystem. The issue involves possible long runtimes for zero-only width values in cross-reference streamsuntimes for zero-only width values in cross-reference streams. Remediation is available by upgrading affected packages to version 6.12.0.

CVE-2026-48156 at a Glance

CVE Identifier CVE-2026-48156
GHSA Identifier GHSA-248m-82v9-q6g6
Severity MODERATE
CVSS v3.1 Base Score 3.3
CWE Classification CWE-834: Excessive Iteration
Affected Product pypdf
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 3.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L).

Attack Vector Local (AV:L)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability Low (A:L)

How to Fix CVE-2026-48156

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: 6.12.0 
pip install pypdf>=6.12.0
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-2026-48156, 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 6.12.0), 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-834: Excessive Iteration, where the product performs an iteration or loop without sufficiently limiting the number of times that the loop is executed. 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. This requires cross-reference streams with `/W [0 0 0]` values and large `/Size` values. ### Patches This has been fixed in [pypdf==6.12.0](https://github.com/py-pdf/pypdf/releases/tag/6.12.0). ### Workarounds If developers are unable to upgrade their apps immediately, they should consider applying the changes from PR [#3791](https://github.com/py-pdf/pypdf/pull/3791).

CVE-2026-48156 Affected pypdf Versions

1 component(s)
Fixed Versions:
6.12.0
Product / Package Ecosystem Affected Versions Fixed Version
pypdf
pypi/pypdf
PyPI
< 6.12.0
6.12.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/py-pdf/pypdf/security/advisories/GHSA-248m-82v9-q6g6
NVD — CVE-2026-48156 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-48156
pypdf Source Repository REPOSITORY
https://github.com/py-pdf/pypdf/pull/3791
Security Fix Commit FIX COMMIT
https://github.com/py-pdf/pypdf/commit/507d7c9aa6ea83389b954b9c3c0c528fe5d5da70
pypdf Source Repository REPOSITORY
https://github.com/py-pdf/pypdf
pypdf Release RELEASE
https://github.com/py-pdf/pypdf/releases/tag/6.12.0

Frequently Asked Questions

What is CVE-2026-48156?
CVE-2026-48156 is a security vulnerability in pypdf involving Possible long runtimes for zero-only width values in cross-reference streamsuntimes for zero-only width values in cross-reference streams under CWE-834: Excessive Iteration.
Which pypdf versions are affected?
Affected versions include releases prior to 6.12.0 across affected packages: pypdf.
What version fixes CVE-2026-48156?
Upgrading to 6.12.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pypdf affected?
Yes, pypdf is affected in releases prior to 6.12.0. Upgrade your dependency to 6.12.0 or later.
What is the CVSS score of CVE-2026-48156?
CVE-2026-48156 has a CVSS v3.1 base score of 3.3 (MODERATE) with vector string CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L.
What CWE is associated with CVE-2026-48156?
CVE-2026-48156 is classified under CWE-834: Excessive Iteration (The product performs an iteration or loop without sufficiently limiting the number of times that the loop is executed.).
How can I check PyPI dependencies for CVE-2026-48156?
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-248m-82v9-q6g6",
  "modified" : "2026-06-12T18:29:59Z",
  "published" : "2026-06-12T18:29:59Z",
  "aliases" : [ "CVE-2026-48156" ],
  "summary" : "pypdf: Possible long runtimes for zero-only width values in cross-reference streamsuntimes for zero-only width values in cross-reference streams",
  "details" : "### Impact\n\nAn attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires cross-reference streams with `/W [0 0 0]` values and large `/Size` values.\n\n### Patches\n\nThis has been fixed in [pypdf==6.12.0](https://github.com/py-pdf/pypdf/releases/tag/6.12.0).\n\n### Workarounds\n\nIf developers are unable to upgrade their apps immediately, they should consider applying the changes from PR [#3791](https://github.com/py-pdf/pypdf/pull/3791).",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/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" : "6.12.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/py-pdf/pypdf/security/advisories/GHSA-248m-82v9-q6g6"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-48156"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/py-pdf/pypdf/pull/3791"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/py-pdf/pypdf/commit/507d7c9aa6ea83389b954b9c3c0c528fe5d5da70"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/py-pdf/pypdf"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/py-pdf/pypdf/releases/tag/6.12.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-834" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-12T18:29:59Z",
    "nvd_published_at" : "2026-05-28T16:16:29Z"
  }
}