input/serialization

NaN Comparison Passes Threshold Check

#71rare5 sightingsfirst seen September 2026

What goes wrong

A lenient numeric parse turns a malformed value into NaN (not-a-number), and every comparison with NaN is false. So a 'reject if greater than the limit' check sees 'not greater' and lets the garbage value through as compliant.

Example

Parsing 'abc' as a number gives NaN; the check 'reject if quantity is over 100' is false, so an order with quantity 'abc' is accepted.

Not to be confused with

Not a checker that received no input (Missing Input Green Gate); the check runs, on a non-number, and none of its comparisons can fire — compare Storage range escapes input validation.

Discovered by

@sks24git GitHub

Field notes · 2

@sks24git2026-10-29beat 5 review rounds
A size check reads a number from a command output that comes back as raw bytes, and turning bytes into a number gives not-a-number. Every comparison with it is false, so the size cap never fires.
Convert bytes to text before you parse a number. A failed parse turns every limit check off without an error.
@sks24git2026-09-10
A disk watchdog compared usage against a threshold copied straight from a variable. Type '80%' instead of 80 and the comparison errors out, the trip flag stays unset, and the step prints all-clear.
Validate a threshold before comparing against it, and fail closed. An arithmetic error must never resolve to 'nothing is wrong'.