Seldaek/monolog · error · InvalidArgumentException

Headers can not contain newline characters for security reas

Error message

Headers can not contain newline characters for security reasons

What it means

Error "Headers can not contain newline characters for security reasons" thrown in Seldaek/monolog.

Source

Thrown at src/Monolog/Handler/NativeMailerHandler.php:88

    {
        parent::__construct($level, $bubble);
        $this->to = (array) $to;
        $this->subject = $subject;
        $this->addHeader(sprintf('From: %s', $from));
        $this->maxColumnWidth = $maxColumnWidth;
    }

    /**
     * Add headers to the message
     *
     * @param  string|string[] $headers Custom added headers
     * @return $this
     */
    public function addHeader($headers): self
    {
        foreach ((array) $headers as $header) {
            if (strpos($header, "\n") !== false || strpos($header, "\r") !== false) {
                throw new \InvalidArgumentException('Headers can not contain newline characters for security reasons');
            }
            $this->headers[] = $header;
        }

        return $this;
    }

    /**
     * Add parameters to the message
     *
     * @param  string|string[] $parameters Custom added parameters
     * @return $this
     */
    public function addParameter($parameters): self
    {
        $this->parameters = array_merge($this->parameters, (array) $parameters);

        return $this;

View on GitHub (pinned to 57eb102834)

When it happens

Trigger: Thrown at src/Monolog/Handler/NativeMailerHandler.php:88 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Seldaek/monolog@57eb102834 (2026-08-17). Data as JSON: /api/errors/1233efbb0c46a241. Report an issue: GitHub.