AIKIDO-2026-597441

TL;DR

The OpenQASM 2 importer functions qiskit.qasm2.load and qiskit.qasm2.loads parse classical expressions with a recursive operator-precedence parser. When given a program containing deeply nested expressions, such as an arbitrarily long run of parentheses, the expression subparser recurses without bound and exhausts the native stack. This causes a stack-overflow segmentation fault that abruptly crashes the interpreter process, allowing a denial of service through crafted OpenQASM 2 input. The fix threads a recursion-depth limit derived from sys.getrecursionlimit() through the parser and raises a Python RecursionError before the stack is exhausted.