CVE-2020-13625 is a high-severity (CVSS 7.5) CWE-116 vulnerability in phpmailer/phpmailer. 1 public exploit reference exists, so weaponization risk is real. A fix is available for phpmailer/phpmailer — see the affected versions and patch details below.
Insufficient output escaping of attachment names in PHPMailer
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2020-13625 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
phpmailer/phpmailerReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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:
- Open an issue in the PHPMailer repo
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | phpmailer/phpmailer | all versions | 6.1.6composer require phpmailer/phpmailer:^6.1.6 |
Affected Products
ubuntu linuxcanonicaldebian linuxdebianfedorafedoraprojectphpmailerphpmailer_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for phpmailer/phpmailer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update phpmailer/phpmailer to 6.1.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-13625 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is CVE-2020-13625 in your dependencies?
Find it across Packagist, including transitive dependencies.