GCVE-110-CERTCC-2025-263614

## Overview The npm package *expr-eval* is a JavaScript library that evaluates mathematical expressions and is used in various applications, including NLP and AI. A vulnerability in this library has been disclosed that could allow arbitrary code execution by an attacker using maliciously crafted input. ## Description The npm projects *expr-eval* and *expr-eval-fork* are JavaScript libraries used to parse and evaluate mathematical expressions, extending NLP applications that process mathematical expressions and their numerical data. This capability is particularly useful in generative AI systems that need to interpret mathematical expressions within user prompts. The `Parser` class and its `evaluate()` method is designed to provide user-defined expressions in a safer way than JavaScript’s native `eval()` function. This design choice is critical for npm-based projects, especially those running in server environments where access to a system's local resources could pose security risks. According to [npmjs.com](https://www.npmjs.com/package/expr-eval), *expr-eval* has over 250 dependent packages, including integrations such as *oplangchain*, a JavaScript implementation of the popular LangChain framework. The related project *expr-eval-fork* was created to address a prior [Prototype Pollution vulnerability (Issue #266)](https://github.com/silentmatt/expr-eval/issues/266) that remained unresolved in the original *expr-eval* repository, which appears to be unmaintained by the original author, with last release date of 2019-09-28. A newly discovered vulnerability allows an attacker to define arbitrary functions within the `context` object used by the parser. This capability can be exploited to inject malicious code that executes system-level commands, potentially accessing sensitive local resources or exfiltrating data. This issue has been patched via [Pull Request #288](https://github.com/silentmatt/expr-eval/pull/288). The vulnerability is tracked with [CVE-2025-12735](https://www.cve.org/CVERecord?id=CVE-2025-12735), as well as the GitHub Advisory [GHSA-jc85-fpwf-qm7x](https://github.com/advisories/GHSA-jc85-fpwf-qm7x). These identifiers enable automated tools such as `npm audit` to detect the vulnerability in affected projects. The [CVE-2025-13204](https://www.cve.org/CVERecord?id=CVE-2025-13204) has also been published for the earlier [Prototype Pollution vulnerability](Prototype Pollution vulnerability) identified in 2021 that is not fixed in *expr-eval*, however the *expr-eval-fork* released in 2024-01-10. ## Impact An attacker with the ability to influence input fields processed by *expr-eval* can craft malicious payloads that trigger arbitrary command execution on the host system. This constitutes a *Technical Impact = Total* under the [SSVC](https://certcc.github.io/SSVC/reference/decision_points/technical_impact/) framework, meaning: > The vulnerability gives the adversary total control over the behavior of the software or total disclosure of all information on the affected system. ## Solution Developers and Users are advised either to: 1. *Apply the security patch* from [Pull Request #288](https://github.com/silentmatt/expr-eval/pull/288), or 2. *Upgrade to the latest patched version* of the *expr-eval* or *expr-eval-fork* package as they become available. The newly released [expr-eval-fork 3.0.1](hhttps://www.npmjs.com/package/expr-eval-fork/v/3.0.1 ) has been tested to resolve this issue. Note: The patch introduces: * A defined *AllowList* of safe functions accessible via `evaluate()` * A mandatory *registration mechanism* for custom functions. * Updated test cases ensuring enforcement of these constraints can be understood and applied ## Acknowledgements Thanks to the reporter Jangwoo Choe (UKO) for responsibly disclosing this issue. Thanks to [huydoppaze](https://github.com/huydoppaz) for improving the suggested patch. We also acknowledge *GitHub Security* and *npm* for their proactive security advisories and automated vulnerability audits. This document was written by Vijay Sarvepalli and Renae Metcalf.