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Insufficient output escaping of attachment names in PHPMailer

High severity GitHub Reviewed Published May 27, 2020 in PHPMailer/PHPMailer • Updated Jan 20, 2023

Package

composer phpmailer/phpmailer (Composer)

Affected versions

< 6.1.6

Patched versions

6.1.6

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:

References

@Synchro Synchro published to PHPMailer/PHPMailer May 27, 2020
Reviewed May 27, 2020
Published to the GitHub Advisory Database May 27, 2020
Published by the National Vulnerability Database Jun 8, 2020
Last updated Jan 20, 2023

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS score

0.630%
(79th percentile)

Weaknesses

CVE ID

CVE-2020-13625

GHSA ID

GHSA-f7hx-fqxw-rvvj

Source code

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