CVE-2021-34551: Phpmailer/phpmailer Remote Code Execution Vulnerability

HIGH
Advisory Identifier: GHSA-7q44-r25x-wm4q
CVSS 8.1
CWE-94 CWE-434
Published
Advisory Summary

CVE-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

CVE Identifier CVE-2021-34551
GHSA Identifier GHSA-7q44-r25x-wm4q
Severity HIGH
CVSS v3.1 Base Score 8.1
CWE Classification CWE-94: Improper Control of Generation of Code ('Code Injection')
Affected Product Phpmailer/phpmailer
Package Ecosystem Packagist
Published Date
Last Updated

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).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (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.

phpmailer/phpmailer fixed: 6.5.0
Upgrade phpmailer/phpmailer to 6.5.0
Verify Direct and Transitive Dependencies

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

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. ### Impact Arbitrary code may be run by a remote attacker under the web server or PHP process running on Window hosts. ### Patches Mitigated in PHPMailer 6.5.0 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. ### Workarounds Any of: * Ensure that calling code does not pass unfiltered user-supplied data to the `$lang_path` parameter of the `setLanguage()` method. * Block or filter the use of unknown UNC paths in this parameter (or altogether). * Ensure that unauthorised users do not have the ability to read from unknown remote servers via UNC paths. * Run on an OS that does not support UNC paths ### References [CVE-2021-34551](https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-34551). Reported by [listensec.com](https://listensec.com) via Tidelift. ### For more information If you have any questions or comments about this advisory: * Open an issue in [PHPMailer](https://github.com/PHPMailer/PHPMailer) * [Email the maintainers](mailto:phpmailer@synchromedia.co.uk)

CVE-2021-34551 Affected Phpmailer/phpmailer Versions

1 component(s)
Fixed Versions:
6.5.0
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?
CVE-2021-34551 is a security vulnerability in Phpmailer/phpmailer involving Remote Code Execution vulnerability in PHPMailer 6.4.1 running on Windows under CWE-94: Improper Control of Generation of Code ('Code Injection').
Which Phpmailer/phpmailer versions are affected?
Affected versions include releases prior to 6.5.0 across affected packages: phpmailer/phpmailer.
What version fixes CVE-2021-34551?
Upgrading to 6.5.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is phpmailer/phpmailer affected?
Yes, phpmailer/phpmailer is affected in releases prior to 6.5.0. Upgrade your dependency to 6.5.0 or later.
What is the CVSS score of CVE-2021-34551?
CVE-2021-34551 has a CVSS v3.1 base score of 8.1 (HIGH) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-34551?
CVE-2021-34551 is classified under CWE-94: Improper Control of Generation of Code ('Code Injection') (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.).
How can I check Packagist dependencies for CVE-2021-34551?
Run the dependency tree command: 'inspect dependencies for phpmailer/phpmailer'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
{
  "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"
  }
}