Compliance Impact

This vulnerability can compromise the confidentiality, integrity, and availability of affected systems by allowing remote attackers to execute heap-based buffer overflow attacks. Such compromises can lead to unauthorized access or data breaches, which may result in non-compliance with standards and regulations like GDPR and HIPAA that require protection of sensitive data and system integrity. Therefore, failure to patch this vulnerability could negatively impact compliance with these regulations. [1]

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Executive Summary

CVE-2026-0821 is a heap-based buffer overflow vulnerability in the QuickJS JavaScript engine (quickjs-ng versions up to 0.11.0). It occurs in the function `js_typed_array_constructor` when constructing typed arrays. An attacker can define a malicious getter on the prototype of the constructor that resizes or detaches the underlying ArrayBuffer during construction. This causes the constructor to operate on stale or invalid buffer data, leading to out-of-bounds memory access and a heap buffer overflow. The vulnerability can be exploited remotely without authentication, potentially allowing attackers to execute arbitrary code or cause crashes. [1, 2, 3]

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Impact Analysis

This vulnerability can compromise the confidentiality, integrity, and availability of systems using the affected QuickJS engine. Exploiting the heap buffer overflow can allow attackers to execute arbitrary code remotely, crash applications, or corrupt memory, leading to denial of service or unauthorized access. Since the exploit is publicly available and requires no authentication, systems are at high risk if unpatched. [1]

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Detection Guidance

Detection of CVE-2026-0821 involves monitoring for exploitation attempts targeting the js_typed_array_constructor function in quickjs-ng QuickJS versions up to 0.11.0. Since the vulnerability is triggered by JavaScript code that manipulates typed arrays with side effects (such as resizing or detaching ArrayBuffers), detection can include: 1) Using AddressSanitizer (ASAN) or similar memory error detection tools when running QuickJS to catch heap buffer overflow errors. 2) Monitoring logs or crash reports for heap-buffer-overflow errors related to typed array operations. 3) Reviewing GitHub issue #1296 for reproduction steps and PoC code that can be used to test your environment. 4) Running the provided test case (e.g., tests/bug1296.js) that triggers the vulnerability to verify if your QuickJS version is vulnerable. Specific commands are not explicitly provided in the resources, but using ASAN with QuickJS and running the PoC or test scripts from the GitHub repository can help detect the vulnerability. [3]

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Mitigation Strategies

The immediate mitigation step is to apply the official patch for CVE-2026-0821, identified by commit c5d80831e51e48a83eab16ea867be87f091783c5 on the quickjs-ng GitHub repository. This patch adds re-validation of the ArrayBuffer state after side effects during typed array construction, preventing out-of-bounds access and heap buffer overflow. Users should update their quickjs-ng QuickJS engine to a version including this fix or manually apply the patch. Additionally, avoid running untrusted JavaScript code that constructs typed arrays with potentially malicious prototype getters until the patch is applied. Monitoring for public proof-of-concept exploits and restricting remote access to vulnerable QuickJS instances can also reduce risk. [1, 4, 5]

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