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`

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.