FinallySkipped

(legacy summary: finally blocks can fail to execute in one script block and control still proceed to another.)

Effect

Object can be observed in an inconsistent state if they can be tricked into calling out to code that causes an exception that is never caught.

Assumptions

• Sensitive code uses try finally to preserve its correctness.
• Those pieces of code are reachable without control being inside the body of a try statement with a catch statement.
• That sensitive code can be tricked into causing an exception after inside a critical section guarded by a finally. Stack overflows result in exceptions.

Versions

• IE6 and possibly later.

Examples

On IE 6,

try {
  ;
} finally {
  alert('Finally');
}

alerts "Finally," and

try {
  throw new Error();
} catch (e) {
  throw e;
} finally {
  alert('Finally');
}

also alerts but the below which should be semantically equivalent

try {
  throw new Error();
} finally {
  alert('Finally');
}

does not.