octobercms/october · error · Twig\Sandbox\SecurityNotAllowedMethodError

Writing to reserved session key "%s" is blocked in Safe Mode

Error message

Writing to reserved session key "%s" is blocked in Safe Mode.

What it means

Error "Writing to reserved session key "%s" is blocked in Safe Mode." thrown in octobercms/october.

Source

Thrown at modules/system/twig/securitypolicy/SafeSessionStore.php:119

     */
    protected function assertKeyAllowed(string $method, $key): void
    {
        if (is_array($key)) {
            foreach (array_keys($key) as $k) {
                $this->assertKeyAllowed($method, $k);
            }
            return;
        }

        if (!is_string($key) || $key === '') {
            return;
        }

        $topKey = strstr($key, '.', true) ?: $key;

        foreach ($this->reservedKeyPrefixes as $prefix) {
            if (str_starts_with($topKey, $prefix)) {
                throw new SecurityNotAllowedMethodError(
                    sprintf('Writing to reserved session key "%s" is blocked in Safe Mode.', $key),
                    Store::class,
                    $method
                );
            }
        }
    }
}

View on GitHub (pinned to b608633a7e)

When it happens

Trigger: Thrown at modules/system/twig/securitypolicy/SafeSessionStore.php:119 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of octobercms/october@b608633a7e (2026-08-21). Data as JSON: /api/errors/090c36dad461db63. Report an issue: GitHub.