CVE-2026-27888
📋 TL;DR
This vulnerability in pypdf allows attackers to craft malicious PDF files that cause denial of service by exhausting system RAM when the XFA property is accessed and the corresponding stream uses FlateDecode compression. Anyone using pypdf versions before 6.7.3 to process PDF files is affected, particularly applications that parse untrusted PDF input.
💻 Affected Systems
- pypdf
📦 What is this software?
Pypdf by Pypdf Project
⚠️ Risk & Real-World Impact
Worst Case
Complete system unavailability due to RAM exhaustion, potentially causing service disruption, data loss, or system crashes.
Likely Case
Denial of service affecting the application processing the PDF, causing service interruption and potential resource exhaustion on the host system.
If Mitigated
Limited impact with proper input validation and resource limits, though processing of malicious PDFs would still fail.
🎯 Exploit Status
Exploitation requires only the ability to provide a malicious PDF file to the vulnerable application.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 6.7.3
Vendor Advisory: https://github.com/py-pdf/pypdf/security/advisories/GHSA-x7hp-r3qg-r3cj
Restart Required: No
Instructions:
1. Update pypdf using pip: pip install --upgrade pypdf==6.7.3
2. Verify the update completed successfully
3. Test PDF processing functionality
🔧 Temporary Workarounds
Manual patch application
allApply the security patch from the GitHub commit to your local pypdf installation
git clone https://github.com/py-pdf/pypdf.git
cd pypdf
git checkout 7a4c8246ed48d9d328fb596942271da47b6d109c
pip install -e .
🧯 If You Can't Patch
- Implement strict input validation to reject PDFs with XFA forms or FlateDecode compression
- Deploy resource limits (memory, CPU) on processes that handle PDF parsing
🔍 How to Verify
Check if Vulnerable:
Check pypdf version: python -c "import pypdf; print(pypdf.__version__)" and compare to 6.7.3Check Version:
python -c "import pypdf; print(pypdf.__version__)"Verify Fix Applied:
After updating, verify version is 6.7.3 or higher and test with known malicious PDF samples📡 Detection & Monitoring
Log Indicators:
- Memory exhaustion alerts
- Process crashes during PDF parsing
- High RAM usage by Python processes
Network Indicators:
- Multiple PDF uploads to vulnerable endpoints
- Unusual PDF file patterns
SIEM Query:
source="application_logs" AND ("pypdf" OR "PDF processing") AND ("crash" OR "memory" OR "out of memory")