mXparser is a feature-rich mathematical expression parser for the JVM and .NET. It handles a large library of built-in functions (trigonometric, hyperbolic, special, probability, combinatorial), operators, iterated and summation operators, physical and mathematical constants, and user-defined elements: Argument, Constant, and Function objects the host registers on the Expression before parsing.
Despite the breadth, mXparser is still a mathematics engine. It evaluates to a numeric result and has no mechanism to reference Java classes, construct objects, invoke methods, or reach reflection, Runtime, or ProcessBuilder. An injected mXparser expression therefore does not produce code execution, and shell-command payloads are not valid syntax in the grammar. Describe the impact honestly: the vector is the mathematical surface and the host-defined elements, not the JVM.
Vulnerable pattern#
// formula supplied in the request
Expression ex = new Expression(formula);
ex.addArguments(new Argument("x", xValue));
double result = ex.calculate();
The intended input is an arithmetic formula in x. The raw string reaches the parser, so an attacker supplies any expression mXparser accepts.
Exposed user-defined elements#
The reachable context is whatever the application registered. User-defined Arguments and Constants are readable by name, so an injected expression can surface a value the interface never intended to expose by naming it directly. User-defined Functions added with addFunctions(...) are callable with attacker-chosen arguments:
pricing(0) + secretMargin
As with any math engine, mXparser does nothing dangerous on its own; the registered function reaches exactly as far as the host implemented it. Probing which identifiers evaluate versus which leave the expression in an error state (mXparser returns NaN and exposes getErrorMessage()) enumerates the available arguments, constants, and functions.
mXparser also parses expressions that build up its own user-defined elements inline, including the function-definition and iteration syntax, which widens the grammar an injected string can exercise but keeps it inside the numeric model.
Resource exhaustion#
The context-independent abuse is forcing expensive evaluation. Iterated operators over large ranges do substantial work per request, for example a summation across a huge index span:
sum(i, 1, 100000000, i^2)
Deeply nested functions, large factorials and gamma evaluations, and expressions engineered to return NaN or infinite values push computation cost and can propagate degenerate numbers into downstream application logic. The impact is availability and corrupted results, contained within the evaluator.