CVE-2025-24359: ASTEVAL Vulnerable to Maliciously Crafted Format Strings Leading to Sandbox Escape
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.
Classification
CVE ID: CVE-2025-24359
CVSS Base Severity: HIGH
CVSS Base Score: 8.4
Affected Products
Vendor: lmfit
Product: asteval
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.05% (probability of being exploited)
EPSS Percentile: 17.97% (scored less or equal to compared to others)
EPSS Date: 2025-02-21 (when was this score calculated)
References
https://github.com/lmfit/asteval/security/advisories/GHSA-3wwr-3g9f-9gc7https://github.com/lmfit/asteval/blob/cfb57f0beebe0dc0520a1fbabc35e66060c7ea71/asteval/asteval.py#L507
https://lucumr.pocoo.org/2016/12/29/careful-with-str-format