CVE-2026-71870 in pypdf
Summary
by MITRE • 08/07/2026
pypdf is a free and open-source pure-python PDF library. Prior to 6.15.0, a crafted PDF can cause large memory consumption when pypdf/_cmap.py function parse_bfrange parses unusually large source-code or destination-string tokens in a font /ToUnicode CMap during text extraction. This issue is fixed in 6.15.0.
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Analysis
by VulDB Data Team • 08/07/2026
The vulnerability in pypdf affects versions prior to 6.15.0 and represents a significant memory consumption issue that can lead to resource exhaustion during PDF text extraction operations. This flaw specifically manifests when the library processes crafted PDF files containing malformed font mapping data within the /ToUnicode CMap structure. The vulnerability resides in the pypdf/_cmap.py module where the parse_bfrange function handles source-code and destination-string tokens during font decoding processes. When encountering unusually large token values, the parsing mechanism consumes excessive memory resources proportional to the size of these malformed tokens rather than processing them efficiently within reasonable memory bounds.
The technical exploitation of this vulnerability occurs when a malicious PDF file contains specially crafted CMap entries with oversized source or destination strings that trigger unbounded memory allocation within the parse_bfrange function. This behavior creates a denial-of-service condition where system resources become consumed rapidly, potentially leading to application crashes or system instability. The issue stems from inadequate input validation and memory management within the font mapping parsing logic, allowing attackers to craft PDF files that cause the library to allocate memory proportional to the size of malicious token values rather than implementing reasonable limits or bounds checking.
From an operational perspective, this vulnerability poses significant risks to applications that process untrusted PDF content, particularly those in document processing systems, web applications, or automated PDF analysis tools. The impact extends beyond simple resource exhaustion as it can affect system availability and performance, potentially allowing attackers to consume all available memory on systems running vulnerable versions of pypdf. This makes the vulnerability particularly dangerous in server environments where multiple PDF processing operations might be occurring simultaneously, as the memory consumption could cascade across multiple concurrent processes.
The fix implemented in version 6.15.0 addresses this issue through enhanced input validation and memory management within the parse_bfrange function. Security researchers have classified this type of vulnerability under CWE-770, which covers allocation of resources without limits or with inadequate limits, and it aligns with ATT&CK technique T1499.002 for resource exhaustion attacks. Organizations should immediately upgrade to pypdf version 6.15.0 or later to mitigate this risk, as the fix implements proper bounds checking and memory allocation limits that prevent the excessive consumption patterns observed in vulnerable versions. Additionally, implementing proper PDF validation and sanitization measures at the application level can provide additional defense-in-depth protection against similar vulnerabilities in other components of the document processing pipeline.
This vulnerability highlights the importance of robust input validation in parsing libraries and demonstrates how seemingly innocuous font mapping data within PDF files can be exploited to create resource exhaustion conditions. The issue serves as a reminder that even well-established open-source libraries require continuous security monitoring and timely patching to address emerging threats in document processing environments where untrusted content is routinely handled.