Package Instance

Insufficient output escaping of attachment names in PHPMailer
### Impact
CWE-116: Incorrect output escaping.

An attachment added like this (note the double quote within the attachment name, which is entirely valid):

    $mail->addAttachment('/tmp/attachment.tmp', 'filename.html";.jpg');

Will result in a message containing these headers:

    Content-Type: application/octet-stream; name="filename.html";.jpg"
    Content-Disposition: attachment; filename="filename.html";.jpg"

The attachment will be named `filename.html`, and the trailing `";.jpg"` will be ignored. Mail filters that reject `.html` attachments but permit `.jpg` attachments may be fooled by this.

Note that the MIME type itself is obtained automatically from the *source filename* (in this case `attachment.tmp`, which maps to a generic `application/octet-stream` type), and not the *name* given to the attachment (though these are the same if a separate name is not provided), though it can be set explicitly in other parameters to attachment methods.

### Patches
Patched in PHPMailer 6.1.6 by escaping double quotes within the name using a backslash, as per RFC822 section 3.4.1, resulting in correctly escaped headers like this:

    Content-Type: application/octet-stream; name="filename.html\";.jpg"
    Content-Disposition: attachment; filename="filename.html\";.jpg"

### Workarounds
Reject or filter names and filenames containing double quote (`"`) characters before passing them to attachment functions such as `addAttachment()`.

### References
[CVE-2020-13625](https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2020-13625).
[PHPMailer 6.1.6 release](https://github.com/PHPMailer/PHPMailer/releases/tag/v6.1.6)

### For more information
If you have any questions or comments about this advisory:
* Open an issue in [the PHPMailer repo](https://github.com/PHPMailer/PHPMailer/issues)

Remote Code Execution vulnerability in PHPMailer 6.4.1 running on Windows
PHPMailer 6.4.1 contains a possible remote code execution vulnerability through the `$lang_path` parameter of the `setLanguage()` method. If the `$lang_path` parameter is passed unfiltered from user input, it can be set to [a UNC path](https://docs.microsoft.com/en-us/dotnet/standard/io/file-path-formats#unc-paths), and if an attacker is also able to create a remote mount on the server that the UNC path points to, a script file under their control may be executed. 

### Impact
Arbitrary code may be run by a remote attacker under the web server or PHP process running on Window hosts.

### Patches
Mitigated in PHPMailer 6.5.0 by no longer treating translation files as PHP code, but by parsing their text content directly.
This approach avoids the possibility of executing unknown code while retaining backward compatibility. This isn't ideal, so the current translation format is deprecated and will be replaced in the next major release.

### Workarounds
Any of:
* Ensure that calling code does not pass unfiltered user-supplied data to the `$lang_path` parameter of the `setLanguage()` method.
* Block or filter the use of unknown UNC paths in this parameter (or altogether).
* Ensure that unauthorised users do not have the ability to read from unknown remote servers via UNC paths.
* Run on an OS that does not support UNC paths

### References
[CVE-2021-34551](https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-34551).

Reported by [listensec.com](https://listensec.com) via Tidelift.

### For more information
If you have any questions or comments about this advisory:
* Open an issue in [PHPMailer](https://github.com/PHPMailer/PHPMailer)
* [Email the maintainers](mailto:phpmailer@synchromedia.co.uk)

Object injection
PHPMailer is vulnerable to an object injection attack.

PHPMailer untrusted code may be run from an overridden address validator
If a function is defined that has the same name as the default built-in email address validation scheme (`php`), it will be called in default configuration as when no validation scheme is provided, the default scheme's callable `php` was being called. If an attacker is able to inject such a function into the application (a much bigger issue), it will be called whenever an email address is validated, such as when calling `validateAddress()`.

### Impact
Low impact – exploitation requires that an attacker can already inject code into an application, but it provides a trigger pathway.

### Patches
This is patched in PHPMailer 6.5.0 by denying the use of simple strings as validator function names, which is a very minor BC break.

### Workarounds
Inject your own email validator function.

### References
Reported by [Vikrant Singh Chauhan](mailto:vi@hackberry.xyz) via [huntr.dev](https://www.huntr.dev/).
[CVE-2021-3603](https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-3603)

### For more information
If you have any questions or comments about this advisory:
* Open an issue in [the PHPMailer project](https://github.com/PHPMailer/PHPMailer)
* [Email us](mailto:phpmailer@synchromedia.co.uk).

XSS vulnerability in code example
The `code_generator.phps` example does not filter user input prior to output. This file is distributed with a `.phps` extension, so it it not normally executable unless it is explicitly renamed, so it is safe by default. There's also an undisclosed potential XSS vulnerability in the default exception handler (unused by default).