CVE-2020-13625

Insufficient output escaping of attachment names in PHPMailer

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:

• Open an issue in the PHPMailer repo

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.

CVE-2020-13625 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (6.1.6); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

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"

1. What is CVE-2020-13625? CVE-2020-13625 is a high-severity security vulnerability in phpmailer/phpmailer (composer), affecting versions < 6.1.6. It is fixed in 6.1.6.
2. How severe is CVE-2020-13625? CVE-2020-13625 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of phpmailer/phpmailer are affected by CVE-2020-13625? phpmailer/phpmailer (composer) versions < 6.1.6 is affected.
4. Is there a fix for CVE-2020-13625? Yes. CVE-2020-13625 is fixed in 6.1.6. Upgrade to this version or later.
5. Is CVE-2020-13625 exploitable, and should I be worried? Whether CVE-2020-13625 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2020-13625 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2020-13625? Upgrade phpmailer/phpmailer to 6.1.6 or later.

Other vulnerabilities in phpmailer/phpmailer