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PHPMailer 6.4.1 and earlier contain a vulnerability that can result in untrusted code being called (if such code is injected into the host project's scope by other means). If the $patternselect parameter to validateAddress() is set to 'php' (the default, defined by PHPMailer::$validator), and the global namespace contains a function called php, it will be called in preference to the built-in validator of the same name. Mitigated in PHPMailer 6.5.0 by denying the use of simple strings as validator function names. Recorded as CVE-2021-3603. Reported by Vikrant Singh Chauhan via huntr.dev.

PHPMailer versions 6.4.1 and earlier contain 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, and if an attacker is also able to persuade the server to load a file from that UNC path, a script file under their control may be executed. This vulnerability only applies to systems that resolve UNC paths, typically only Microsoft Windows. PHPMailer 6.5.0 mitigates this 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. Recorded as CVE-2021-34551. Reported by Jilin Diting Information Technology Co., Ltd via Tidelift.

PHPMailer versions between 6.1.8 and 6.4.0 contain a regression of the earlier CVE-2018-19296 object injection vulnerability as a result of a fix for Windows UNC paths in 6.1.8. Recorded as CVE-2020-36326. Reported by Fariskhi Vidyan via Tidelift. 6.4.1 fixes this issue, and also enforces stricter checks for URL schemes in local path contexts.

PHPMailer versions 6.1.5 and earlier contain an output escaping bug that occurs in Content-Type and Content-Disposition when filenames passed into addAttachment and other methods that accept attachment names contain double quote characters, in contravention of RFC822 3.4.1. No specific vulnerability has been found relating to this, but it could allow file attachments to bypass attachment filters that are based on matching filename extensions. Recorded as CVE-2020-13625. Reported by Elar Lang of Clarified Security.

PHPMailer versions prior to 6.0.6 and 5.2.27 are vulnerable to an object injection attack by passing phar:https:// paths into addAttachment() and other functions that may receive unfiltered local paths, possibly leading to RCE. Recorded as CVE-2018-19296. See this article for more info on this type of vulnerability. Mitigated by blocking the use of paths containing URL-protocol style prefixes such as phar:https://. Reported by Sehun Oh of cyberone.kr.

PHPMailer versions prior to 5.2.24 (released July 26th 2017) have an XSS vulnerability in one of the code examples, CVE-2017-11503. The code_generator.phps example did 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, and the file is not included when PHPMailer is loaded through composer, so it is safe by default. There was also an undisclosed potential XSS vulnerability in the default exception handler (unused by default). Patches for both issues kindly provided by Patrick Monnerat of the Fedora Project.

PHPMailer versions prior to 5.2.22 (released January 9th 2017) have a local file disclosure vulnerability, CVE-2017-5223. If content passed into msgHTML() is sourced from unfiltered user input, relative paths can map to absolute local file paths and added as attachments. Also note that addAttachment (just like file_get_contents, passthru, unlink, etc) should not be passed user-sourced params either! Reported by Yongxiang Li of Asiasecurity.

PHPMailer versions prior to 5.2.20 (released December 28th 2016) are vulnerable to CVE-2016-10045 a remote code execution vulnerability, responsibly reported by Dawid Golunski, and patched by Paul Buonopane (@Zenexer).

PHPMailer versions prior to 5.2.18 (released December 2016) are vulnerable to CVE-2016-10033 a remote code execution vulnerability, responsibly reported by Dawid Golunski.

PHPMailer versions prior to 5.2.14 (released November 2015) are vulnerable to CVE-2015-8476 an SMTP CRLF injection bug permitting arbitrary message sending.

PHPMailer versions prior to 5.2.10 (released May 2015) are vulnerable to CVE-2008-5619, a remote code execution vulnerability in the bundled html2text library. This file was removed in 5.2.10, so if you are using a version prior to that and make use of the html2text function, it's vitally important that you upgrade and remove this file.

PHPMailer versions prior to 2.0.7 and 2.2.1 are vulnerable to CVE-2012-0796, an email header injection attack.

Joomla 1.6.0 uses PHPMailer in an unsafe way, allowing it to reveal local file paths, reported in CVE-2011-3747.

PHPMailer didn't sanitise the $lang_path parameter in SetLanguage. This wasn't a problem in itself, but some apps (PHPClassifieds, ATutor) also failed to sanitise user-provided parameters passed to it, permitting semi-arbitrary local file inclusion, reported in CVE-2010-4914, CVE-2007-2021 and CVE-2006-5734.

PHPMailer 1.7.2 and earlier contained a possible DDoS vulnerability reported in CVE-2005-1807.

PHPMailer 1.7 and earlier (June 2003) have a possible vulnerability in the SendmailSend method where shell commands may not be sanitised. Reported in CVE-2007-3215.