Phpmailer
CVE-2021-34551
HIGH
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V5 - File Handling File type validation, storage isolation
MITRE ATT&CK
2 techniques across 2 tactics: Command and Control, Persistence The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS score of 8.1 (HIGH). Attack characteristics: network attack vector, high complexity, no privileges required, no user interaction not required. |
| Exploit ScenarioDerived | A remote attacker could upload malicious files that can be executed on the server by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability. |
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Alert meAnalysisAI
PHPMailer before 6.5.0 on Windows allows remote code execution if lang_path is untrusted data and has a UNC pathname. Rated high severity (CVSS 8.1), this vulnerability is remotely exploitable, no authentication required. No vendor patch available.
RemediationAI
No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Validate file types server-side, store uploads outside webroot, use random filenames, scan for malware.
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in composer
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability is classified as Unrestricted File Upload (CWE-434), which allows attackers to upload malicious files that can be executed on the server. PHPMailer before 6.5.0 on Windows allows remote code execution if lang_path is untrusted data and has a UNC pathname. Affected products include: Phpmailer Project Phpmailer, Fedoraproject Fedora. Version information: before 6.5.0.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
PHPMailer before 6.5.0 on Windows allows remote code execution if lang_path is untrusted data and has a UNC pathname.
Threat Intelligence Overview
NVD
CVE.org
EPSS
GitHub
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Malicious file upload attacks exploit insufficient validation when web applications accept user-provided files.
Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.
Affected Products (CPE)NVD
The mailSend function in the isMail transport in PHPMailer before 5.2.18 might allow remote attackers to pass extra para
The isMail transport in PHPMailer before 5.2.20 might allow remote attackers to pass extra parameters to the mail comman
PHPMailer before 6.1.6 contains an output escaping bug when the name of a file attachment contains a double quote charac
PHPMailer 5.2.23 has XSS in the "From Email Address" and "To Email Address" fields of code_generator.php. Rated medium s
An issue was discovered in PHPMailer before 5.2.22. Rated medium severity (CVSS 5.5), this vulnerability is low attack c
PHPMailer before 5.2.27 and 6.x before 6.0.6 is vulnerable to an object injection attack. Rated high severity (CVSS 8.8)
PHPMailer 6.4.1 and earlier contain a vulnerability that can result in untrusted code being called (if such code is inje
Multiple CRLF injection vulnerabilities in PHPMailer before 5.2.14 allow attackers to inject arbitrary SMTP commands via
Exploit-DB