CVE-2026-24819: Weixin4j Memory Allocation Vulnerability

CVE-2026-24819 Overview

CVE-2026-24819 is an Improperly Controlled Sequential Memory Allocation vulnerability (CWE-1325) affecting the foxinmy weixin4j Java library. This vulnerability exists within the weixin4j-base/src/main/java/com/foxinmy/weixin4j/util modules, specifically associated with the CharArrayBuffer.Java and ClassUtil.Java program files.

The weixin4j library is a Java SDK for WeChat development, and this memory allocation flaw could allow remote attackers to manipulate memory allocation patterns through network-accessible attack vectors.

Critical Impact
Remote attackers may exploit improper sequential memory allocation controls to cause resource exhaustion or potentially leak sensitive information from affected weixin4j deployments.

Affected Products

weixin4j (weixin4j-base module)
Applications utilizing weixin4j CharArrayBuffer.Java
Applications utilizing weixin4j ClassUtil.Java

Discovery Timeline

2026-01-27 - CVE-2026-24819 published to NVD
2026-01-27 - Last updated in NVD database

Technical Details for CVE-2026-24819

Vulnerability Analysis

This vulnerability stems from improper controls over sequential memory allocation operations within the weixin4j utility classes. CWE-1325 (Improperly Controlled Sequential Memory Allocation) describes scenarios where a product allocates memory in a sequential manner without adequate controls to limit the total amount of memory consumed.

In the context of weixin4j, the affected files CharArrayBuffer.Java and ClassUtil.Java may allow an attacker to trigger excessive memory allocation through crafted inputs processed via network requests. The vulnerability can be exploited remotely without requiring authentication or user interaction, though it requires specific preconditions to be met for successful exploitation.

Root Cause

The root cause lies in the CharArrayBuffer.Java and ClassUtil.Java utility classes within the weixin4j-base module. These classes implement sequential memory allocation patterns that lack proper bounds checking or resource limits. When processing external input, the allocation logic may not properly validate or constrain the amount of memory being requested, allowing attackers to influence memory consumption behavior.

Attack Vector

The attack vector is network-based, requiring no special privileges or user interaction. An attacker can send specially crafted requests to an application using the vulnerable weixin4j library. The attack requires certain preconditions (AT:P in CVSS 4.0 vector) to be present for successful exploitation.

The exploitation flow involves:

Identifying an application using the vulnerable weixin4j library
Crafting input that triggers the vulnerable code paths in CharArrayBuffer.Java or ClassUtil.Java
Sending the malicious input via network requests
Causing improper memory allocation that may lead to information disclosure from the vulnerable system or subsequent system impact

For technical implementation details, refer to the GitHub Pull Request #229 which addresses this vulnerability.

Detection Methods for CVE-2026-24819

Indicators of Compromise

Unusual memory consumption patterns in Java applications using weixin4j
Unexpected growth in heap allocation within CharArrayBuffer or ClassUtil class instances
Application performance degradation or OutOfMemoryError exceptions linked to weixin4j utility operations

Detection Strategies

Monitor Java heap usage for applications utilizing weixin4j dependencies
Implement application-level logging to track memory allocation patterns in weixin4j utility classes
Use Java profiling tools to identify abnormal object allocation in com.foxinmy.weixin4j.util package
Review application dependencies for vulnerable versions of weixin4j

Monitoring Recommendations

Configure JVM monitoring to alert on unusual memory consumption spikes
Implement application performance monitoring (APM) to track weixin4j module behavior
Set up garbage collection logging to identify potential memory allocation abuse patterns
Monitor for repeated requests that could indicate exploitation attempts

How to Mitigate CVE-2026-24819

Immediate Actions Required

Review all applications for weixin4j library dependencies, particularly the weixin4j-base module
Apply the fix from GitHub Pull Request #229
Implement network-level controls to limit request rates and sizes to applications using weixin4j
Consider temporarily isolating affected applications if patching is not immediately possible

Patch Information

The fix for this vulnerability is available via Pull Request #229 on the weixin4j GitHub repository. Organizations should review this pull request and apply the patched version of the library to their applications.

After updating, rebuild and redeploy all applications that depend on the weixin4j-base module to ensure the fix is applied.

Workarounds

Implement input validation and size limits at the application layer before data reaches weixin4j utility classes
Configure JVM memory limits to constrain the impact of potential memory exhaustion
Deploy web application firewalls (WAF) with request size limits for applications using weixin4j
Isolate vulnerable applications in network segments with restricted access until patching is complete

bash

# Configuration example: Set JVM memory limits to constrain potential memory exhaustion
# Apply these flags when starting your Java application using weixin4j

java -Xmx512m -Xms256m \
     -XX:+HeapDumpOnOutOfMemoryError \
     -XX:HeapDumpPath=/var/log/heapdumps/ \
     -jar your-weixin4j-application.jar