Symfony UX is a JavaScript ecosystem for Symfony. From 2.8.0 until 2.36.0 and 3.1.0, when a #[LiveProp] is typed as DateTimeInterface and no explicit format is configured, Symfony\UX\LiveComponent\LiveComponentHydrator::hydrateObjectValue() falls back to new $className($value), allowing client-supplied relative strings such as now, tomorrow, or +10 years to move a writable, format-less date prop past time-based business logic checks. This issue is fixed in versions 2.36.0 and 3.1.0.

Affected: Packagist: symfony/ux-live-component

### Description

When a `#[LiveProp]` is typed as a `DateTimeInterface` and no explicit `format` is configured, `Symfony\UX\LiveComponent\LiveComponentHydrator::hydrateObjectValue()` falls back to `new $className($value)`. The `DateTime` / `DateTimeImmutable` constructors accept relative strings such as `"now"`, `"tomorrow"`, or `"+10 years"`, so a writable, format-less date prop can be pushed to an arbitrary point in time by the client. Components that rely on a date prop to gate time-based business logic can be moved past those checks by a frontend payload that no maintainer would consider a valid date.

### Resolution

`hydrateObjectValue()` now parses format-less date props strictly with `createFromFormat(DateTimeInterface::RFC3339, ...)`, matching the format already emitted by `dehydrateObjectValue()`. Normal round-trips are unaffected; only inputs that aren't valid RFC 3339 are now rejected, which is consistent with how a format-configured prop already behaved.

The patch for this issue is available [here](https://github.com/symfony/ux/commit/d24d78fda6df2d5964312255943ebf3a217b79a2) for branch 2.x (and forward-ported to 3.x).

### Credits

Symfony would like to thank Pascal Cescon for reporting the issue and Hugo Alliaume for providing the fix.