CVE-2026-113794 in pypdf
Summary
by MITRE • 10/22/2026
pypdf is a free and open-source pure-python PDF library. Prior to 6.20.0, an attacker can craft an incomplete PDF that ends inside a standard cross-reference table, causing pypdf to mishandle the unexpected end of file and enter an infinite loop. This issue is fixed in version 6.20.0.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified within the pypdf library represents a significant availability risk stemming from improper input validation during PDF parsing operations. As a widely used pure-Python library for manipulating PDF documents, pypdf processes complex file structures that include cross-reference tables to map object locations within the document. The core technical flaw lies in the parser's handling of truncated or malformed files where the data stream terminates prematurely inside a standard cross-reference table section. Instead of detecting this incomplete state and raising an appropriate exception or error code, the library enters an infinite loop while attempting to resolve offsets that do not exist due to the abrupt end of file condition. This behavior indicates a failure in boundary checking logic within the parsing routine, allowing malformed input to disrupt normal program execution flow indefinitely.
From a security architecture perspective, this flaw aligns with CWE-835, which describes loops involving resource exhaustion, and CWE-20, indicating improper input validation. The infinite loop consumes CPU resources continuously without progressing or terminating, effectively creating a denial of service condition for any application relying on pypdf to process untrusted PDF files. In operational environments where automated document processing pipelines ingest external inputs, such as email attachments or user uploads, this vulnerability can be exploited by an attacker crafting a specifically designed malicious PDF file. By submitting a truncated cross-reference table structure, the attacker forces the parsing engine into a non-terminating state, thereby rendering the associated service unresponsive and potentially impacting other processes sharing system resources through CPU saturation.
The impact of this vulnerability extends beyond simple application freezing to broader infrastructure stability concerns in high-throughput environments. Services that batch-process documents or handle multiple concurrent requests may experience cascading failures if worker threads are blocked indefinitely by such malformed inputs. This aligns with the MITRE ATT&CK technique T1496, Resource Hijacking, specifically under the sub-technique of CPU consumption for denial of service purposes. The lack of a timeout mechanism or depth limit in the parsing logic exacerbates the severity, as there is no automatic recovery path once the infinite loop condition is triggered.
Mitigation strategies primarily involve upgrading to version 6.20.0 or later, where the developers have implemented fixes to detect and handle unexpected end-of-file conditions gracefully within cross-reference table processing routines. For systems unable to upgrade immediately, implementing input validation at the ingestion layer can provide a defensive workaround. This includes checking file integrity via checksums before parsing, enforcing strict size limits on uploaded documents, or utilizing sandboxed execution environments with CPU time quotas to prevent any single process from monopolizing system resources indefinitely. Additionally, integrating timeout wrappers around PDF processing functions can ensure that long-running parse operations are terminated if they exceed expected duration thresholds, thereby preserving service availability even in the presence of malformed inputs.