CVE-2026-106452 in lz4-java
Summary
by MITRE • 10/06/2026
yawkat LZ4 Java provides LZ4 compression for Java. Prior to 1.11.2, net.jpountz.lz4.LZ4BlockInputStream refill() validates that the compressedLen field in a legacy LZ4Block header is nonnegative but allocates a compressed-input buffer of that attacker-controlled size before reading payload data, allowing a header-only stream to request a near-2 GiB allocation and exhaust the JVM heap. Canonical writers emit raw blocks when compression is not smaller than the original block, but vulnerable readers accept non-canonical oversized compressed blocks. This issue is fixed in version 1.11.2.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified in yawkat LZ4 Java prior to version 1.11.2 represents a critical resource exhaustion flaw rooted in improper input validation and buffer allocation logic within the decompression stream handler. The library, which provides LZ4 compression capabilities for Java applications, processes data through the net.jpountz.lz4.LZ4BlockInputStream class. Specifically, the refill method is responsible for reading headers and allocating memory buffers required to hold compressed data before it is actually read from the input stream. In vulnerable versions of the software, this process contains a significant logical error where the system validates that the compressedLen field in the legacy LZ4Block header is non-negative but fails to verify whether the requested size is reasonable or within expected bounds relative to available resources. This oversight allows an attacker to craft a maliciously formatted input stream containing a header with a near-maximum integer value for the compressed length, effectively requesting an allocation of nearly two gigabytes of memory from the Java Virtual Machine heap without providing corresponding payload data.
This architectural flaw leads directly to a Denial of Service condition by exhausting system resources. Because the buffer is allocated based solely on the attacker-controlled header field before any actual data validation or reading occurs, a small amount of malicious input can trigger a massive memory allocation request. If the JVM does not have sufficient heap space available to satisfy this request, it will throw an OutOfMemoryError, causing the application to crash or become unresponsive. This is particularly dangerous in server-side environments where LZ4 decompression might be used for processing incoming network requests or file uploads, as a single malicious packet can destabilize the entire service instance. The issue highlights a common pitfall in high-performance compression libraries where performance optimizations bypass standard safety checks regarding input size relative to expected output ratios.
The vulnerability is further exacerbated by the library's handling of non-canonical data structures. Canonical LZ4 writers are designed to emit raw blocks when the compressed data is not smaller than the original block, ensuring efficiency and consistency. However, vulnerable readers in versions prior to 1.11.2 do not enforce this canonical behavior strictly enough during decompression validation. They accept oversized compressed blocks that deviate from standard encoding practices, allowing attackers to exploit these non-standard inputs for resource exhaustion attacks. This lack of strict adherence to expected data formats creates an attack surface where malformed or maliciously crafted streams can bypass normal processing logic and trigger the flawed allocation routine.
From a classification perspective, this vulnerability aligns with CWE-789: Memory Allocation with Excessive Size Value, as it involves allocating memory based on untrusted input without adequate bounds checking. It also relates to CWE-400: Uncontrolled Resource Consumption, where an attacker can cause the system to consume excessive amounts of resources leading to service disruption. In terms of offensive security frameworks such as MITRE ATT&CK, this behavior is consistent with techniques used in Denial of Service attacks, specifically those targeting resource exhaustion through malformed input processing. The attack vector typically involves sending a specially crafted LZ4 stream over a network connection or providing it via file upload mechanisms that are processed by the vulnerable library components.
Mitigation for this vulnerability requires an immediate upgrade to version 1.11.2 of yawkat LZ4 Java, which addresses these allocation flaws by implementing stricter validation checks on input sizes before buffer allocation occurs. Developers integrating this library should ensure their build pipelines enforce dependency updates and verify that the latest stable release is in use across all services relying on LZ4 decompression. Additionally, application-level defenses such as setting strict limits on maximum allowed payload sizes for incoming requests can provide a secondary layer of protection against resource exhaustion attempts. Security teams should monitor JVM heap usage metrics closely during periods of high traffic or after deploying updates to ensure that the fix effectively prevents excessive memory allocation under adversarial conditions.