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.
PHPMailer 6.1.6 release
For more information
If you have any questions or comments about this advisory:
References
Impact
CWE-116: Incorrect output escaping.
An attachment added like this (note the double quote within the attachment name, which is entirely valid):
Will result in a message containing these headers:
The attachment will be named
filename.html, and the trailing";.jpg"will be ignored. Mail filters that reject.htmlattachments but permit.jpgattachments 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 genericapplication/octet-streamtype), 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:
Workarounds
Reject or filter names and filenames containing double quote (
") characters before passing them to attachment functions such asaddAttachment().References
CVE-2020-13625.
PHPMailer 6.1.6 release
For more information
If you have any questions or comments about this advisory:
References