CVE-2026-28804 — pypdf
Fix: py-pdf/pypdf@648c627CVE-2026-28804 is a CWE-407 vulnerability in pypdf. A fix is available for pypdf — see the affected versions and patch details below.
pypdf: Inefficient decoding of ASCIIHexDecode streams
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-2026-28804.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
pypdfReal-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 accessing a stream which uses the /ASCIIHexDecode filter.
Patches
This has been fixed in pypdf==6.7.5.
Workarounds
If you cannot upgrade yet, consider applying the changes from PR #3666.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | pypdf | all versions | 6.7.5pip install --upgrade 'pypdf==6.7.5' |
Affected Products
pypdfpy-pdfDetection & mitigation playbook
Open-source dependencyDetect
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 6.7.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28804 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.
To mitigate this issue, avoid processing untrusted PDF documents with applications that use the pypdf library. If processing untrusted PDFs is unavoidable, consider sandboxing the application responsible for PDF processing to limit potential resource exhaustion.Source: Red Hat security advisory for CVE-2026-28804 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-28804 in your dependencies?
Find it across PyPI, including transitive dependencies.