CVE-2026-41314 Overview
CVE-2026-41314 is a Memory Exhaustion vulnerability affecting pypdf, a free and open-source pure-python PDF library. An attacker can craft a malicious PDF file that leads to complete RAM exhaustion when processed by vulnerable versions of the library. This denial of service condition is triggered when the library attempts to process an image using /FlateDecode with excessively large size values.
Critical Impact
Processing a specially crafted PDF document can cause memory exhaustion, leading to application crashes and denial of service conditions on systems running vulnerable pypdf versions.
Affected Products
- pypdf versions prior to 6.10.2
- Applications and services that process PDF files using vulnerable pypdf versions
- Python-based document processing pipelines utilizing pypdf
Discovery Timeline
- April 22, 2026 - CVE-2026-41314 published to NVD
- April 22, 2026 - Last updated in NVD database
Technical Details for CVE-2026-41314
Vulnerability Analysis
This vulnerability is classified under CWE-789 (Memory Allocation with Excessive Size Value). The flaw exists in how pypdf handles image decompression when processing PDF files that utilize the FlateDecode filter. FlateDecode is a standard PDF compression method based on the zlib/deflate algorithm, commonly used to compress embedded images and streams within PDF documents.
When pypdf encounters an image stream with /FlateDecode compression, it allocates memory based on size parameters specified in the PDF. The vulnerability arises because the library fails to properly validate these size values before memory allocation. An attacker can craft a PDF with artificially inflated size values for image dimensions, causing the library to attempt allocation of enormous amounts of memory—far beyond what would be reasonable for any legitimate image.
The attack requires local access (the victim must open or process the malicious PDF) and some user interaction, making it suitable for targeted attacks via email attachments, file uploads, or document processing services.
Root Cause
The root cause is insufficient validation of image size parameters within the FlateDecode stream handling code. The library trusts the size values declared in the PDF structure without implementing proper bounds checking or sanity limits on memory allocation requests.
Prior to the fix, when pypdf processed a FlateDecode image stream, it would extract the declared width and height parameters and calculate the required memory for the decompressed image data. Without validation, an attacker could specify extremely large dimension values (e.g., width and height of millions of pixels), causing the library to attempt memory allocations measured in gigabytes or more.
Attack Vector
The attack vector is local, requiring an attacker to deliver a malicious PDF file to the target system. Common delivery mechanisms include:
The attacker creates a PDF document containing an embedded image stream with the /FlateDecode filter. Within this stream's metadata, they specify extremely large size values for the image dimensions. When a vulnerable application using pypdf attempts to parse or extract this image, the library allocates memory based on these malicious size values.
The malicious PDF structure would contain a stream object with FlateDecode compression and deliberately oversized dimension declarations in the image dictionary. When pypdf processes this stream and attempts to decompress the image data, it allocates memory proportional to the declared image size, leading to memory exhaustion. For detailed technical information on the vulnerability mechanism and the specific code changes, refer to the GitHub Security Advisory.
Detection Methods for CVE-2026-41314
Indicators of Compromise
- Sudden memory spikes when processing PDF documents
- Application crashes or out-of-memory errors during PDF parsing operations
- Python processes consuming abnormally high amounts of RAM
- PDF files with unusually small file sizes but containing image streams with extremely large declared dimensions
Detection Strategies
- Monitor pypdf library versions in your Python environments and flag any installations below 6.10.2
- Implement resource limits on processes that handle PDF parsing to contain potential memory exhaustion attacks
- Analyze incoming PDF files for suspicious FlateDecode streams with disproportionate size declarations relative to actual compressed data size
- Deploy application-level monitoring to detect rapid memory consumption patterns during document processing
Monitoring Recommendations
- Set up memory threshold alerts for services that process PDF documents using pypdf
- Implement logging for PDF processing operations to track file sources when memory anomalies occur
- Monitor Python dependency manifests across your organization for outdated pypdf versions
How to Mitigate CVE-2026-41314
Immediate Actions Required
- Upgrade pypdf to version 6.10.2 or later immediately in all affected environments
- Audit your Python projects and dependency trees to identify all pypdf installations
- Implement memory limits on containers or processes that handle PDF processing as a defense-in-depth measure
- Consider implementing file size and complexity checks before processing untrusted PDF documents
Patch Information
The vulnerability has been addressed in pypdf version 6.10.2. The fix introduces proper validation and bounds checking for image size parameters when processing FlateDecode streams, preventing excessive memory allocation. The patch is available through the GitHub Release 6.10.2, and the specific code changes can be reviewed in the GitHub Commit and Pull Request #3734.
Workarounds
- Apply the patch changes manually from the referenced commit if immediate upgrade is not feasible
- Implement application-level memory limits using operating system controls (ulimit, cgroups) or container resource constraints
- Pre-screen PDF files using alternative tools before processing with pypdf
- Restrict PDF processing to trusted document sources where possible
# Upgrade pypdf to the patched version
pip install --upgrade pypdf>=6.10.2
# Verify installed version
pip show pypdf | grep Version
# For requirements.txt, update the minimum version
# pypdf>=6.10.2
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
