Remote code execution via class-resource type probing
Published Jul 23, 2026 · Updated Jul 23, 2026
Deserialization in Alibaba Group Fastjson 1.2.68 through 1.2.83 allows remote attackers to execute code via crafted JSON. ParserConfig.checkAutoType probes an attacker-controlled @type value as a class resource and trusts a discovered @JSONType annotation, enabling nested JAR URL class loading. Exploitation requires a network-reachable JSON parsing path in a Spring Boot executable fat-JAR with SafeMode disabled and runs code with the Java process's privileges.
Summary
What happened
Deserialization in Alibaba Group Fastjson 1.2.68 through 1.2.83 allows remote attackers to execute code via crafted JSON. ParserConfig.checkAutoType probes an attacker-controlled @type value as a class resource and trusts a discovered @JSONType annotation, enabling nested JAR URL class loading. Exploitation requires a network-reachable JSON parsing path in a Spring Boot executable fat-JAR with SafeMode disabled and runs code with the Java process's privileges.
The record
- CVE
- CVE-2026-16723
- Published
- Jul 23, 2026
- Updated
- Jul 23, 2026
- Vendor
- Alibaba Group
- Product
- Fastjson
- Classifications
- CWE-20, CWE-502, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 23, 2026CVE publishedPublication date reported by the CVE source.
- Jul 23, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=1.2.68 <=1.2.83
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Fastjson 1.2.83 remote code execution analysis and exploitfunctional · demonstrated
- EQSTLab CVE-2026-16723 Fastjson RCEfunctional · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Reported exploitation
- ThreatBook TDP captured in-the-wild exploitationreported exploitation
- Imperva-observed Fastjson exploitation attemptsreported exploitation
Technologies
Your stack
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Your stack
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