How severe is CVE-2026-48156?

No CVSS score has been assigned to CVE-2026-48156 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-48156?

CVE-2026-48156 affects the following packages: pypdf (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-48156?

Update pypdf to 6.12.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48156 is resolved across your whole dependency graph.

How do I detect CVE-2026-48156 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-2026-48156 if there is no patch (or I can't update yet)?

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.

Is CVE-2026-48156 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-48156 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-2026-48156?

CVE-2026-48156 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 6th 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-2026-48156?

CVE-2026-48156 is classified as CWE-834 (CWE-834). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-48156 published, and has it been updated?

CVE-2026-48156 was published on May 28, 2026 and was last updated on October 21, 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-2026-48156 — pypdf

Fix: py-pdf/pypdf#3791

CVE-2026-48156 is a CWE-834 vulnerability in pypdf. A fix is available for pypdf — see the affected versions and patch details below.

pypdf: Possible long runtimes for zero-only width values in cross-reference streams

Also known asGHSA-248m-82v9-q6g6PYSEC-2026-3004

Published

May 28, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 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-2026-48156.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs6th percentile — riskier than 6% 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 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.

Workarounds

If developers are unable to upgrade their apps immediately, they should consider applying the changes from PR #3791.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`pypdf`	all versions	6.12.0`pip install --upgrade 'pypdf==6.12.0'`

Affected Products

1 product · 1 configurations

Application

pypdfpypdf_project

< 6.12.0

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 6.12.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48156 is resolved across your whole dependency graph.
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.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatLow

This flaw has a Low impact. Red Hat products that process PDF files using the pypdf library are vulnerable to a denial of service. An attacker could provide a specially crafted PDF, causing applications to experience prolonged processing times and potential resource exhaustion. This risk is limited to scenarios where…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-48156 (CC BY 4.0)

Frequently Asked Questions

### 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).

O3 Security · Impact-Aware SCA

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