CVE-2026-55244

## Summary An attacker who can supply expressions to `asteval.Interpreter.eval()` can raise `SystemExit`, `KeyboardInterrupt`, `GeneratorExit`, or `BaseException` from inside the sandbox. These exceptions are subclasses of `BaseException` but not `Exception`, so they bypass the `except Exception:` safety net in both `run()` and `eval()`. The exception propagates verbatim to the calling application, terminating the process or disrupting signal and cleanup handlers. This is distinct from prior vulnerabilities CVE-2025-24359 (format string injection) and GHSA-vp47-9734-prjw (AST mutation TOCTOU), both fixed in 1.0.6. This vector is present in all versions including 1.0.6 and current HEAD. --- ## Affected Code **`asteval/astutils.py`, lines 89–108** — `FROM_PY` exposes dangerous classes to sandbox users: ```python FROM_PY = ('ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', # ← escapes except Exception: 'BufferError', 'BytesWarning', ... 'GeneratorExit', # ← escapes except Exception: ... 'KeyboardInterrupt', # ← escapes except Exception: ... 'SystemExit', # ← escapes except Exception: ...) ``` **`asteval/asteval.py`, line 322** — `run()` exception handler: ```python except Exception: # ← does NOT catch BaseException subclasses if with_raise and self.expr is not None: self.raise_exception(node, expr=self.expr) ``` **`asteval/asteval.py`, line 370** — `eval()` exception handler: ```python except Exception: # ← same gap if show_errors and not raise_errors: ... ``` **`asteval/asteval.py`, line 264** — `raise_exception()` raises the class directly: ```python raise exc(self.error_msg) # ← when exc=SystemExit, escapes both handlers above ``` --- ## Root Cause Python's exception hierarchy has two distinct branches under `BaseException`: