CVE-2025-24359: ASTEVAL Vulnerable to Maliciously Crafted Format Strings Leading to Sandbox Escape

Vulnerability summary

CVE-2025-24359 is a high (CVSS 8.4) vulnerability in lmfit asteval. EPSS estimates a 0.28% chance of exploitation in the next 30 days, higher than 20.3% of scored vulnerabilities.

Timeline

1. 24-01-2025
   PublishedVulnerability first disclosed.
2. 12-02-2025
   Last modifiedVulnerability information updated.

Description

ASTEVAL is an evaluator of Python expressions and statements. Prior to version 1.0.6, if an attacker can control the input to the `asteval` library, they can bypass asteval's restrictions and execute arbitrary Python code in the context of the application using the library. The vulnerability is rooted in how `asteval` performs handling of `FormattedValue` AST nodes. In particular, the `on_formattedvalue` value uses the dangerous format method of the str class. The code allows an attacker to manipulate the value of the string used in the dangerous call `fmt.format(__fstring__=val)`. This vulnerability can be exploited to access protected attributes by intentionally triggering an `AttributeError` exception. The attacker can then catch the exception and use its `obj` attribute to gain arbitrary access to sensitive or protected object properties. Version 1.0.6 fixes this issue.

• CWE-134Use of Externally-Controlled Format StringThe product uses a function that accepts a format string as an argument, but the format string originates from an external source.
• CWE-749Exposed Dangerous Method or FunctionThe product provides an Applications Programming Interface (API) or similar interface for interaction with external actors, but the interface includes a dangerous method or function that is not properly restricted.