Executive Summary

The vulnerability in the Zed Attack Proxy (ZAP) ViewState add-on before version 4 is an insecure deserialization flaw. It allows attackers who control a proxied web server to execute arbitrary code by embedding a malicious serialized Java object in the javax.faces.ViewState HTTP response parameter.

The JSFViewState.decode() method base64-decodes the ViewState value and directly passes it to ObjectInputStream.readObject() without any deserialization filters, allowlists, or type restrictions. This causes the malicious object to be deserialized inside the ZAP Java Virtual Machine (JVM) when the Desktop UI renders the ViewState panel, potentially leading to arbitrary code execution.

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Impact Analysis

This vulnerability can have severe impacts including allowing remote attackers to execute arbitrary code within the ZAP environment. Since the malicious serialized object is deserialized without restrictions, attackers can potentially run harmful code on the system running ZAP.

The CVSS score of 8.7 (high severity) reflects the significant risk, with impacts on confidentiality, integrity, and availability. This means attackers could compromise sensitive data, alter system behavior, or disrupt services.

Additionally, although no confirmed remote code execution (RCE) has been observed yet due to some mitigations like classloader isolation, future exploits may still be possible. Users are advised to update immediately and consider additional security measures such as running ZAP in a container.

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Detection Guidance

This vulnerability involves the insecure deserialization of malicious serialized Java objects embedded in the javax.faces.ViewState HTTP response parameter when proxied through ZAP ViewState add-on versions prior to 4.

Detection would involve monitoring HTTP responses for the presence of the javax.faces.ViewState parameter containing suspicious or unexpected base64-encoded serialized Java objects.

Since the vulnerability triggers when the ZAP Desktop UI renders the ViewState panel, detection on the system running ZAP could include checking if the ViewState add-on version is prior to 4 and if the JSF ViewState format is enabled.

No explicit commands or automated detection scripts are provided in the available resources.

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Mitigation Strategies

Immediate mitigation steps include updating the ZAP ViewState add-on to version 4 or later, which disables JSF ViewState support and removes the insecure deserialization vector.

If updating is not immediately possible, users should disable the option to view JSF ViewStates in the add-on to prevent deserialization of malicious objects.

Additional recommended precautions include running ZAP in a containerized environment to isolate potential impacts and enabling auto-updates for the add-on to ensure timely patching.

Users of older ZAP versions, especially prior to 2.17, should upgrade to at least 2.17 and update the ViewState add-on accordingly.

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Compliance Impact

The CVE-2026-57527 vulnerability allows attackers to achieve arbitrary code execution by exploiting insecure deserialization in the Zed Attack Proxy (ZAP) ViewState add-on. This can lead to unauthorized access and control over the affected system.

Such unauthorized access and potential data breaches could impact compliance with common standards and regulations like GDPR and HIPAA, which require protection of sensitive data and secure handling of systems to prevent unauthorized access.

However, the provided context and resources do not explicitly discuss or analyze the direct impact of this vulnerability on compliance with these standards.

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