CVE-2026-119207 in pypdf
Summary
by MITRE • 10/29/2026
pypdf is a free and open-source pure-python PDF library. Prior to 6.21.3, pypdf can consume excessive memory when strict mode loads a crafted invalid PDF dictionary. Nested parsing failures add repeated exception text to newly raised errors, allowing a small malformed dictionary to amplify into very large error messages. This issue is fixed in version 6.21.3.
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Analysis
by VulDB Data Team • 10/29/2026
The vulnerability identified within the pypdf library prior to version 6.21.3 represents a significant resource exhaustion risk stemming from improper handling of malformed input data during strict parsing operations. As an open-source pure-Python library designed for PDF manipulation, pypdf is frequently utilized in backend services and document processing pipelines where it must parse complex or potentially maliciously crafted files. The core technical flaw resides in the error handling mechanism employed when the library operates in strict mode with invalid PDF dictionaries. When a malformed dictionary is encountered, the parsing logic triggers nested failures that result in repeated exception text being appended to newly raised errors. This recursive accumulation of error messages causes the memory footprint associated with processing a single small or moderately sized malicious file to expand exponentially, leading to severe performance degradation and potential service disruption.
From an operational perspective, this behavior classifies as a Denial of Service vulnerability due to its ability to consume excessive system resources without requiring authentication or complex exploitation steps beyond submitting a crafted PDF document. The amplification effect allows attackers with minimal effort to trigger high memory consumption on the host server running pypdf. This can lead to application crashes, out-of-memory errors in containerized environments, or general instability in web applications that rely on this library for file uploads and processing. The impact is particularly acute in scenarios where multiple users submit documents simultaneously, as each malformed request contributes to cumulative resource exhaustion, potentially rendering the service unavailable to legitimate users until resources are reclaimed or the process is restarted.
This vulnerability aligns with CWE-400, which describes Uncontrolled Resource Consumption, specifically highlighting how improper input validation and error handling can lead to excessive memory usage. Furthermore, it maps to MITRE ATT&CK technique T1496, Resource Hijacking, where an adversary exploits a system's resources for their own benefit or to disrupt service availability. The specific mechanism of amplifying small inputs into large outputs through recursive exception chaining is a classic pattern in software vulnerabilities that underscores the importance of bounded error handling and strict input sanitization.
To mitigate this risk, organizations utilizing pypdf must immediately upgrade to version 6.21.3 or later, where the developers have addressed the issue by correcting the logic surrounding nested parsing failures and exception message generation. In environments where upgrading is not immediately feasible, implementing resource limits at the infrastructure level can provide a layer of defense. This includes configuring memory quotas for application processes, setting timeouts on file upload operations to limit processing duration, and deploying web application firewalls that inspect incoming PDF files for known malicious patterns or excessive complexity before they reach the parsing engine. Additionally, running pypdf in isolated containers with strict resource constraints can prevent a single malformed document from impacting the broader system stability.