9.8

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2025-12735

CVE-2025-12735: CVE-2025-12735

The expr-eval library is a JavaScript expression parser and evaluator designed to safely evaluate mathematical expressions with user-defined variables. However, due to insufficient input validation, an attacker can pass a crafted context object or use MEMBER of the context object into the evaluate() function and trigger arbitrary code execution.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2025-12735

CVE-2025-12735:

9.8

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
expr-eval	npm	<= 2.0.2
expr-eval-fork	npm	<= 2.0.2

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in the evaluate function of the expr-eval library, which is responsible for evaluating mathematical expressions. The function failed to properly validate functions passed to it via the values object, allowing an attacker to execute arbitrary code. The analysis of the provided patches, particularly commit 955f390dd395f51ecef7a12ae382042a3dac5b45, reveals the core of the vulnerability and its fix. The patch introduces a security check using a new isAllowedFunc helper function within the evaluate function. This check is applied before a function is executed via f.apply(), ensuring that only functions explicitly allowed or marked as safe can be run. The vulnerable code path is within the IFUNCALL instruction handler inside the evaluate function. Therefore, evaluate is the primary function that would appear in a runtime profile during the exploitation of this vulnerability.

Vulnerable functions

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WAF Protection Rules

WAF Rule

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Reasoning

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