INSPECTING ARCHIVED INTELLIGENCE (OUTDATED VERSION).

FastJson RCE Vulnerability Exploit Targeted in Attacks

| 2026-07-27 23:49 CRITICAL HIGH
JSON
Executive Summary AI-generated
The recent incident data reveals a critical vulnerability in the FastJson open-source Java library, allowing remote code execution without user interaction or elevated privileges. This zero-day attack has been linked to various organizations across industries, including financial services, healthcare, computing, retail, and business sectors. The malicious activity was observed by security company ThreatBook, with researchers at Imperva confirming that it targeted a wide range of organizations in the US. The vulnerability stems from the library's type-resolution logic, which performs attacker-controlled resource lookups before enforcing AutoType restrictions. This flaw has been identified as CVE-2026-16723 and is currently not being addressed by vendors due to its lack of maintenance.
Technical Mitigations AI-generated
* Enable SafeMode: Organizations can enable SafeMode with the option `-Dfastjson.parser.safeMode=true` or use `com.alibaba:fastjson:1.2.83_noneautotype` to prevent remote code execution attacks. * Use a patched version of FastJson 1.x: Alibaba has not released a fixed version of FastJson 1.x, but organizations can migrate to the latest version (FastJson 1.x) which is considered safe and secure. * Avoid deserialization with malicious payloads: When using Spring Boot fat-JAR deployments, developers should avoid specifying target classes during deserialization or use `Object` or `Map` fields that do not contain malicious payloads. * Use a non-fat-JAR deployment model: Organizations can switch to non-fat-JAR deployments (e.g., `.jar` files) which are less vulnerable to FastJson attacks.
Technical Observables
Intelligence Metadata
Actors / Malware / CVEs / Campaigns
CVE-2026-16723CVE-2026-16723
Target & Sectors
NORTH_AMERICA NORTH_AMERICA healthcarehealthcare retailretail
Incident Timeline
‎2026/07/20
Threat actors used a FastJson Remote Code Execution (RCE) vulnerability in versions 1.2.68 through 1.2.83 to target US firms across various industries, including Healthcare and Retail.
industry Healthcare
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
industry Retail
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
infrastructure 1.2.68
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
infrastructure 1.2.83
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
organisation ThreatBook
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
organisation Financial Services
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
organisation Computing, Retail, Business
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
‎July 21
Alibaba's July 21 advisory was published following responsible disclosure by FearsOff Cybersecurity.
organisation FearsOff Cybersecurity
Alibaba published its advisory on July 21 following responsible disclosure by Kirill Firsov of FearsOff Cybersecurity.
‎July 22
Hackers used a FastJson Remote Code Execution (RCE) vulnerability to target US firms in the incident.
‎July 23
Hackers used a FastJson Remote Code Execution (RCE) vulnerability to target US firms in July 2023.
‎Jul 25, 2026
Threat actors exploited a FastJson RCE zero-day vulnerability to target US firms.
‎July 25
Threat actors used a FastJson Remote Code Execution (RCE) vulnerability to target US firms.
attribution Hacker News
The Hacker News confirmed on July 25 that the flaw was absent from CISA's current Known Exploited Vulnerabilities catalog .
attribution Known Exploited
The Hacker News confirmed on July 25 that the flaw was absent from CISA's current Known Exploited Vulnerabilities catalog .
tactic T1588.006 - Vulnerabilities
The Hacker News confirmed on July 25 that the flaw was absent from CISA's current Known Exploited Vulnerabilities catalog .
organisation The Hacker News
The Hacker News also found no patched Fastjson 1.x artifact in the project's GitHub tags or Maven Central repository as of July 25.
organisation Maven Central repository
The Hacker News also found no patched Fastjson 1.x artifact in the project's GitHub tags or Maven Central repository as of July 25.
‎2026/07/27
Hackers target US firms in FastJson RCE zero-day attacks.
infrastructure 1.2.83
Version 1.2.83 remains the latest standard 1.x release, while 1.2.83_noneautotype remains the available restricted build.
infrastructure 1.2
Version 1.2.83 remains the latest standard 1.x release, while 1.2.83_noneautotype remains the available restricted build.
organisation ThreatBook
 Swati Khandelwal  Jul 25, 2026 Vulnerability / Application Security Security firms ThreatBook and Imperva say attackers are targeting a critical flaw in Fastjson, Alibaba's JSON library for Java.
organisation Vulnerability / Application Security
 Swati Khandelwal  Jul 25, 2026 Vulnerability / Application Security Security firms ThreatBook and Imperva say attackers are targeting a critical flaw in Fastjson, Alibaba's JSON library for Java.
organisation FearsOff
CVE-2026-16723 was discovered by FearsOff, an offensive security company, which published a technical write-up earlier this month.
organisation CVSS
Tracked as CVE-2026-16723 , the vulnerability carries an Alibaba-assigned CVSS score of 9.0.
infrastructure 1.2.60
Also, FastJson versions 1.2.60 and earlier, and any non-fat-JAR deployments, aren’t affected either.
organisation GitHub
The project has 25,600 stars and 6,400 forks on GitHub, and is especially prevalent in Chinese enterprise software and projects built on Alibaba's platform.
organisation AutoType
The researchers explain that the flaw stems from the library’s type-resolution logic, which performs attacker-controlled resource lookups before enforcing AutoType restrictions.
AutoType can remain disabled, and no classpath gadget is required.
organisation fastjson2
The vulnerable type-resolution logic is not present in fastjson2, which uses an allowlist-first model for polymorphic deserialization and doesn’t rely on the @JSONType annotation as a trust signal.
organisation Imperva
Imperva has also noted that FastJson 1.x is no longer actively maintained, so it’s unlikely it will receive a security update.
organisation EDR
The Picus whitepaper shows how breach and attack simulation tests your SIEM and EDR rules so threats stop slipping by detection.
organisation Fastjson
Firsov traced the issue to Fastjson's type-resolution path.
organisation JAR
His technical analysis also describes a newer-JDK path that downloads a remote JAR and references it through /proc/self/fd .
organisation Tomcat
Alibaba lists plain non-fat JARs, generic uber-JARs, and Tomcat or Jetty WAR deployments as unaffected.
Tactical Metrics
Metrics
infrastructure
‎1.2.68
Software Version
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
Metrics
infrastructure
‎1.2.83
Software Version
The security issue affects FastJson versions 1.2.68 through 1.2.83 and is leveraged in attacks targeting various organizations in the U.S. The malicious activity was observed last week by the agentic security company ThreatBook, and researchers at the business protection company Imperva confirmed that it was "targeting a wide range of organizations, across Financial Services, Healthcare, Computing, Retail, Business, and other industries.
Version 1.2.83 remains the latest standard 1.x release, while 1.2.83_noneautotype remains the available restricted build.
Metrics
infrastructure
‎1.2.60
Software Version
Also, FastJson versions 1.2.60 and earlier, and any non-fat-JAR deployments, aren’t affected either.
Metrics
infrastructure
‎1.2
Software Version
Version 1.2.83 remains the latest standard 1.x release, while 1.2.83_noneautotype remains the available restricted build.
Intelligence Sources
The Hacker News 2026-07-25
BleepingComputer 2026-07-27