CVE-2026-24819: 
Java vulnerability analysis and mitigation

CVE-2026-24819 is an Improperly Controlled Sequential Memory Allocation vulnerability (CWE-1325) in the foxinmy weixin4j Java library, specifically within the weixin4j-base module's CharArrayBuffer.java and ClassUtil.java files. It affects all versions of weixin4j up to and including 1.10.2 (Maven package com.foxinmy:weixin4j-base). The vulnerability was published on January 27, 2026, with a patch merged on May 20, 2025 and the advisory added to the GitHub Advisory Database on January 27–28, 2026. It carries a CVSS v4.0 base score of 6.3 (Medium severity), assigned by GovTech CSG (Github Advisory, Feedly).

The vulnerability stems from two distinct flaws in the weixin4j-base utility module. First, in CharArrayBuffer.java, the ensureCapacity method performs unprotected integer arithmetic when calculating buffer expansion sizes; if this.len + required overflows, the resulting allocation is smaller than needed, potentially causing buffer under-allocation and memory corruption. Second, in ClassUtil.java, the getDefaultClassLoader method accesses the thread context ClassLoader without proper permission checks when a Java Security Manager is present, which can expose class-loading behavior to unauthorized callers. Both issues were addressed in a single pull request (commit d1c8258) merged into the develop branch (GitHub PR #229, Github Advisory).

Successful exploitation can result in limited disclosure of sensitive information (low confidentiality impact on both the vulnerable and subsequent systems), with no direct impact on integrity or availability. The integer overflow in buffer capacity calculations could theoretically lead to memory corruption in the JVM process, while the ClassLoader access flaw may expose internal class-loading details to network-accessible attackers. Recovery is assessed as automatic, and the overall impact is considered moderate given the constrained confidentiality exposure and absence of integrity or availability degradation (Github Advisory, Feedly).

The fix is available in commit d1c8258 merged into the foxinmy/weixin4j develop branch on May 20, 2025; however, the GitHub Advisory notes no formally patched release version exists yet for the Maven package (com.foxinmy:weixin4j-base ≤ 1.10.2 remains listed as affected). Organizations should monitor the upstream repository for a tagged release incorporating this fix and upgrade as soon as one is available. In the interim, consider restricting network access to services using weixin4j, applying Java Security Manager policies to limit ClassLoader access, and monitoring for anomalous memory allocation behavior in affected JVM processes (GitHub PR #229, Github Advisory).

The vulnerability received limited community attention, with automated CVE tracking services (Vulners, VulDB, CIRCL) and a Bluesky CVE bot account picking up the disclosure shortly after publication. A brief technical write-up was published by Infinitsec describing it as an out-of-memory (OOM) issue. No significant vendor statements, notable researcher commentary, or major media coverage has been identified beyond routine aggregation (Feedly).