CVE-2026-82864 in pdf-lib
Summary
by MITRE • 08/31/2026
pdfme pdf-lib versions before 5.5.10 contain an unbounded buffer growth vulnerability in the DecodeStream.ensureBuffer() method that allows attackers to cause denial of service by supplying a crafted PDF with a FlateDecode stream containing a decompression bomb. Attackers can upload a small compressed PDF that decompresses to hundreds of megabytes, exhausting memory and crashing the Node.js process or freezing browser tabs during PDF parsing.
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Analysis
by VulDB Data Team • 08/31/2026
The vulnerability identified in pdf-lib versions prior to 5.5.10 represents a critical unbounded buffer growth flaw located within the DecodeStream.ensureBuffer method. This specific implementation defect allows for the creation of decompression bombs, also known as zip bombs or gzip bombs, which are maliciously crafted documents designed to exploit resource exhaustion mechanisms during data processing. In this context, an attacker can construct a PDF file that utilizes the FlateDecode stream compression algorithm but is structured such that its uncompressed size is exponentially larger than its compressed size. By supplying a small, seemingly innocuous compressed PDF payload, the library attempts to allocate memory for the full decompressed content without verifying whether the resulting buffer size exceeds reasonable limits or available system resources. This lack of bounds checking on the target buffer allocation constitutes a classic uncontrolled resource consumption scenario that undermines the stability and availability of applications relying on this parsing logic.
From an operational perspective, the impact of this vulnerability is severe for any service or application that processes user-uploaded PDF documents. When a crafted FlateDecode stream is processed by vulnerable versions of pdf-lib, the Node.js process or browser tab attempting to parse the document will attempt to allocate memory proportional to the decompressed size rather than the compressed input size. Since modern systems may have gigabytes of available RAM, an attacker can craft a file that appears small in storage but expands into hundreds of megabytes or even gigabytes upon decompression. This sudden and massive allocation request quickly exhausts the heap space allocated to the JavaScript engine, leading to out-of-memory errors. In server-side environments running Node.js, this typically results in the abrupt termination of the process due to memory limits being exceeded. In client-side browser environments, it causes the tab or entire application window to freeze or crash as the event loop is blocked by excessive garbage collection cycles and allocation failures. This effectively constitutes a denial-of-service condition where legitimate users are unable to access services that depend on PDF parsing capabilities.
This vulnerability aligns with CWE-789, which classifies uncontrolled memory allocation resulting in resource consumption without limits or bounds. The attack vector leverages the inherent asymmetry of lossless compression algorithms like FlateDecode, where highly repetitive data can be compressed into a tiny footprint but expands to its original large size upon decompression. By exploiting this characteristic, attackers bypass traditional file size checks that only examine the initial upload size rather than the potential expanded state. The flaw is particularly dangerous because it does not require code execution or privilege escalation; it merely requires the victim application to parse untrusted input using a vulnerable library version. This makes it an efficient and low-effort attack method for disrupting service availability, often categorized under resource exhaustion attacks in threat modeling frameworks.
To mitigate this vulnerability, organizations must immediately upgrade pdf-lib to version 5.5.10 or later, where the DecodeStream.ensureBuffer logic has been patched to enforce strict limits on buffer growth during decompression operations. For applications that cannot update dependencies instantly due to compatibility constraints, defensive coding practices should be implemented at the application layer. This includes implementing custom stream wrappers that monitor the cumulative size of data being written to buffers and throwing an error if a predefined threshold is exceeded before allocation occurs. Additionally, input validation strategies should incorporate checks for compression ratios or maximum expected output sizes based on known document structures. Security teams should also consider deploying web application firewalls with rules capable of detecting anomalous memory usage patterns associated with decompression bombs during PDF processing workflows. Regular auditing of third-party dependencies and maintaining an up-to-date software bill of materials are essential to prevent recurrence of such resource exhaustion vulnerabilities in production environments.