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The vulnerability involves improper control of sequential memory allocation in the weixin4j library, specifically within the CharArrayBuffer.Java and ClassUtil.Java files in the weixin4j-base module. This flaw occurs when the software dynamically allocates memory in a sequential manner without proper bounds checks, leading to uncontrolled memory consumption. In CharArrayBuffer.Java, functions that append or manipulate character arrays may repeatedly allocate memory in a sequence without limiting the allocation size, causing excessive memory usage. Similarly, in ClassUtil.Java, methods that handle class loading or reflection might allocate memory sequentially for class data or metadata without restrictions. Attackers can exploit this by triggering repeated memory allocations through crafted inputs, such as sending large or malformed data packets to endpoints using these components. This can result in memory exhaustion, leading to denial of service (DoS) as the application runs out of available memory. The vulnerability affects all versions of weixin4j, making it critical to apply the available patch to prevent potential abuse. The issue is rooted in the lack of checks on allocation loops or growth factors, allowing memory usage to escalate linearly or exponentially with input size. This type of vulnerability is common in buffer handling code where capacities are increased incrementally without considering system limits. In weixin4j, it impacts modules that process user input or manage internal data structures, potentially affecting service stability and performance. The patch provided in commit d1c8258 addresses this by implementing proper bounds controls and limiting sequential allocations.
Platform: weixin4j
Version: All versions
Vulnerability: Improperly Controlled Sequential Memory Allocation
Severity: Moderate
Date: Jan 27, 2026
Prediction: Patch available Jan 28, 2026
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Reported By: github.com
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