CVE-2025-65570

CriticalPublic PoC

Published: 29 December 2025

Published

29 December 2025

Modified

31 December 2025

KEV Added

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Patch

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CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0017 38.3th percentile

Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2025-65570 is a critical-severity Type Confusion (CWE-843) vulnerability in Jsish Jsish. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 38.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and RA-5 (Vulnerability Monitoring and Scanning).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

SI-2 mandates timely identification, testing, and installation of patches or upgrades for jsish to remediate the type confusion vulnerability in OP_NEXT opcode execution.

SI-16 Memory Protection partial match

prevent

SI-16 implements memory safeguards like ASLR and DEP to mitigate arbitrary code execution from type confusion-induced invalid function pointer reads dependent on heap layout.

RA-5 Vulnerability Monitoring and Scanning partial match

preventdetect

RA-5 requires vulnerability scanning to detect CVE-2025-65570 in jsish deployments and initiate risk-based remediation to prevent remote exploitation.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

The vulnerability allows remote, unauthenticated arbitrary code execution or denial of service in a network-accessible JavaScript interpreter (jsish), directly mapping to exploitation of a public-facing application.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

NVD Description

A type confusion in jsish 2.0 allows incorrect control flow during execution of the OP_NEXT opcode. When an “instanceof” expression uses an array element access as the left-hand operand inside a for-in loop, the instructions implementation leaves an additional array…

reference on the stack rather than consuming it during OP_INSTANCEOF. As a result, OP_NEXT interprets the array as an iterator object and reads the iterCmd function pointer from an invalid structure, potentially causing a crash or enabling code execution depending on heap layout.

Deeper analysisAI

CVE-2025-65570 is a type confusion vulnerability in jsish 2.0, published on 2025-12-29. The issue arises during execution of the OP_NEXT opcode when an "instanceof" expression uses an array element access as the left-hand operand inside a for-in loop. The implementation fails to consume the array reference during OP_INSTANCEOF, leaving it on the stack. Consequently, OP_NEXT misinterprets the array as an iterator object and reads the iterCmd function pointer from an invalid structure, which can lead to a crash or code execution depending on heap layout. It carries a CVSS score of 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) and is associated with CWE-843.

Attackers can exploit this vulnerability remotely over the network with low attack complexity, requiring no privileges, authentication, or user interaction. Successful exploitation allows high-impact confidentiality, integrity, and availability violations, ranging from application crashes to arbitrary code execution contingent on memory layout.

Details on the vulnerability, including a writeup, are provided at https://blog.mcsky.ro/writeups/2025/11/15/inline8-writeup.html. No mitigation or patch information is specified in the available data.