CVE-2021-34551: Phpmailer/phpmailer Remote Code Execution Vulnerability
HIGHCVE-2021-34551 is a HIGH (CVSS 8.1) remote code execution vulnerability (CWE-94: Improper Control of Generation of Code ('Code Injection')) affecting Phpmailer/phpmailer libraries in the Packagist ecosystem. The issue involves remote code execution vulnerability in phpmailer 6.4.1 running on windows. Remediation is available by upgrading affected packages to version 6.5.0.
CVE-2021-34551 at a Glance
Security Impact
CVSS: 8.1
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H).
How to Fix CVE-2021-34551
To remediate this vulnerability, upgrade all affected Phpmailer/phpmailer dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
Upgrade phpmailer/phpmailer to 6.5.0
Run the following command in your project directory to verify that all resolved dependencies use the patched release:
inspect dependencies for phpmailer/phpmailer
How to Check if You Are Affected
To determine whether your application is affected by CVE-2021-34551, inspect your project dependencies for Phpmailer/phpmailer:
inspect dependencies for phpmailer/phpmailer
Analyze the terminal output to locate any version of Phpmailer/phpmailer in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.5.0), your application is affected.
Note: Verify declared build manifests and deployed runtime container environments.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-94: Improper Control of Generation of Code ('Code Injection'), where the product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. In Phpmailer/phpmailer, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2021-34551 Affected Phpmailer/phpmailer Versions
1 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
phpmailer/phpmailer
|
Packagist |
< 6.5.0
|
6.5.0
|
References
Frequently Asked Questions
What is CVE-2021-34551?
Which Phpmailer/phpmailer versions are affected?
What version fixes CVE-2021-34551?
Is phpmailer/phpmailer affected?
What is the CVSS score of CVE-2021-34551?
What CWE is associated with CVE-2021-34551?
How can I check Packagist dependencies for CVE-2021-34551?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-7q44-r25x-wm4q",
"modified" : "2021-06-30T18:13:17Z",
"published" : "2021-06-22T15:17:51Z",
"aliases" : [ "CVE-2021-34551" ],
"summary" : "Remote Code Execution vulnerability in PHPMailer 6.4.1 running on Windows",
"details" : "PHPMailer 6.4.1 contains 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](https://docs.microsoft.com/en-us/dotnet/standard/io/file-path-formats#unc-paths), and if an attacker is also able to create a remote mount on the server that the UNC path points to, a script file under their control may be executed. \n\n### Impact\nArbitrary code may be run by a remote attacker under the web server or PHP process running on Window hosts.\n\n### Patches\nMitigated in PHPMailer 6.5.0 by no longer treating translation files as PHP code, but by parsing their text content directly.\nThis 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.\n\n### Workarounds\nAny of:\n* Ensure that calling code does not pass unfiltered user-supplied data to the `$lang_path` parameter of the `setLanguage()` method.\n* Block or filter the use of unknown UNC paths in this parameter (or altogether).\n* Ensure that unauthorised users do not have the ability to read from unknown remote servers via UNC paths.\n* Run on an OS that does not support UNC paths\n\n### References\n[CVE-2021-34551](https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-34551).\n\nReported by [listensec.com](https://listensec.com) via Tidelift.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [PHPMailer](https://github.com/PHPMailer/PHPMailer)\n* [Email the maintainers](mailto:phpmailer@synchromedia.co.uk)\n",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "Packagist",
"name" : "phpmailer/phpmailer"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "0"
}, {
"fixed" : "6.5.0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/PHPMailer/PHPMailer/security/advisories/GHSA-7q44-r25x-wm4q"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-34551"
}, {
"type" : "WEB",
"url" : "https://github.com/PHPMailer/PHPMailer/commit/acd264bf17ff4ac5c915f0d4226dce8a9ea70bc3"
}, {
"type" : "WEB",
"url" : "https://github.com/FriendsOfPHP/security-advisories/blob/master/phpmailer/phpmailer/CVE-2021-34551.yaml"
}, {
"type" : "WEB",
"url" : "https://github.com/PHPMailer/PHPMailer/blob/master/SECURITY.md"
}, {
"type" : "WEB",
"url" : "https://github.com/PHPMailer/PHPMailer/releases/tag/v6.5.0"
}, {
"type" : "WEB",
"url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/3YRMWGA4VTMXFB22KICMB7YMFZNFV3EJ"
}, {
"type" : "WEB",
"url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/FJYSOFCUBS67J3TKR74SD3C454N7VTYM"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-434", "CWE-94" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2021-06-16T19:50:57Z",
"nvd_published_at" : "2021-06-16T18:15:00Z"
}
}