GHSA-5f37-gxvh-23v6 CVE-2016-10033
Remote code execution in PHPMailer
Critical
Known exploited
Packagist
- Severity
- 9.8 / 10
- Critical · CVSS 3.1
- Exploit chance (EPSS)
- 99.71%
- Chance of exploitation in the next 30 days. Higher than 99.95% of scored vulnerabilities.
- Known exploited
- Yes
- In CISA's catalog since Jul 7, 2025
- Weakness
- CWE-77 Improper Neutralization of Special Elements used in a Command ('Command Injection')
- CWE-88 Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
- Fix
5.2.18- Upgrade phpmailer/phpmailer to this version or later
Exploited in the wild. PHPMailer Command Injection Vulnerability (PHP PHPMailer). Required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Due for U.S. federal agencies by Jul 28, 2025.
Description
Impact
The mailSend function in the default isMail transport in PHPMailer before 5.2.18 might allow remote attackers to pass extra parameters to the mail command and consequently execute arbitrary code via a " (backslash double quote) in a crafted Sender property.
Patches
Fixed in 5.2.18
Workarounds
Filter and validate user input before passing it to internal functions.
References
https://nvd.nist.gov/vuln/detail/CVE-2016-10033 Related to a follow-on issue in https://nvd.nist.gov/vuln/detail/CVE-2016-10045
For more information
If you have any questions or comments about this advisory:
- Open a private issue in the PHPMailer project
Affected versions
Packagist
| Package | Vulnerable | Fixed in |
|---|---|---|
| phpmailer/phpmailer | >= 5.0.0, < 5.2.18 |
5.2.18 |
| phpmailer/phpmailer | >= 5.0.0, < 5.2.18 |
5.2.18 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
phpmailer/phpmailer Packagist → 5.2.18
- composer
composer require phpmailer/phpmailer:^5.2.18
Severity breakdown
CVSS 3.1 9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
- Exploit maturity
- H
Weakness
CWE-77: Improper Neutralization of Special Elements used in a Command ('Command Injection')
The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.
How to prevent it
- Architecture and Design: If at all possible, use library calls rather than external processes to recreate the desired functionality.
- Implementation: If possible, ensure that all external commands called from the program are statically created.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Operation: Run time: Run time policy enforcement may be used in an allowlist fashion to prevent use of any non-sanctioned commands.
- System Configuration: Assign permissions that prevent the user from accessing/opening privileged files.
CWE-88: Improper Neutralization of Argument Delimiters in a Command ('Argument Injection')
The product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.
How to prevent it
- Implementation: Where possible, avoid building a single string that contains the command and its arguments. Some languages or frameworks have functions that support specifying independent arguments, e.g. as an array, which is used to automatically perform the appropriate quoting or escaping while building the command. For example, in PHP, escapeshellarg() can be used to escape a single argument to system(), or exec() can be called with an array of arguments. In C, code can often be refactored from using system() - which accepts a single string - to using exec(), which requires separate function arguments for each parameter.
- Architecture and Design: Understand all the potential areas where untrusted inputs can enter your product: parameters or arguments, cookies, anything read from the network, environment variables, request headers as well as content, URL components, e-mail, files, databases, and any external systems that provide data to the application. Perform input validation at well-defined interfaces.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Implementation: Directly convert your input type into the expected data type, such as using a conversion function that translates a string into a number. After converting to the expected data type, ensure that the input's values fall within the expected range of allowable values and that multi-field consistencies are maintained.
- Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control. Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.
- Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.
- Implementation: When your application combines data from multiple sources, perform the validation after the sources have been combined. The individual data elements may pass the validation step but violate the intended restrictions after they have been combined.
- Testing: Use dynamic tools and techniques that interact with the product using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The product's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
References
Advisories
Packages
Other links
- developer.joomla.org/security-centre/668-20161205-phpmailer-security-advisory.html
- github.com/FriendsOfPHP/security-advisories/blob/master/phpmailer/phpmailer/CVE…
- github.com/PHPMailer/PHPMailer/releases/tag/v5.2.18
- github.com/PHPMailer/PHPMailer/wiki/About-the-CVE-2016-10033-and-CVE-2016-10045…
- drupal.org/psa-2016-004
- packetstormsecurity.com/files/140291/PHPMailer-Remote-Code-Execution.html
- packetstormsecurity.com/files/140350/PHPMailer-Sendmail-Argument-Injection.html
- seclists.org/fulldisclosure/2016/Dec/78
- rapid7.com/db/modules/exploit/multi/http/phpmailer_arg_injection
- exploit-db.com/exploits/42221
- exploit-db.com/exploits/42024
- exploit-db.com/exploits/41996
- exploit-db.com/exploits/41962
- exploit-db.com/exploits/40986
- exploit-db.com/exploits/40974
- exploit-db.com/exploits/40970
- exploit-db.com/exploits/40969
- exploit-db.com/exploits/40968
- cisa.gov/known-exploited-vulnerabilities-catalog
Timeline
- Published
- Added to CISA's Known Exploited Vulnerabilities catalog
- Remediation due for U.S. federal agencies
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-587h-7wmj-h5pm launch-editor: `fs.existsSync()` existence check can be bypassed on Windows | High | Same weakness, CWE-77 |
| CVE-2026-96951 Improper neutralization of special elements used in a command ('command injection') in Windows Shell allows an unauthorized attacker to bypass a security… | High Known exploited | Same weakness, CWE-77 |
| CVE-2026-105134 A flaw has been found in Ahsay AhsayCBS up to 9.15.2.69/10.3.4.44. | Critical Known exploited | Same weakness, CWE-77 |
| GHSA-jf24-8g2h-2wg7 LibreNMS Vulnerable to Remote Code Execution via AboutController | High | Same weakness, CWE-77 |
| GHSA-c9fv-cgmm-2wg7 LibreNMS Vulnerable to Remote Code Execution by Signal Alert Transportation module | High | Same weakness, CWE-77 |
| GHSA-6qc3-v8fv-fv9j Apache Ranger has a Command Injection vulnerability | Critical | Same weakness, CWE-77 |
| GHSA-956x-8gvw-wg5v GitPython: command injection via unguarded Git options in `Repo.archive()`, `git.ls_remote()`, and arbitrary file overwrite via `Repo.iter_commits()` / `Repo.blame()` | High | Same weakness, CWE-77 |
| GHSA-qf6p-p7ww-cwr9 Gogs vulnerable to RCE via git rebase --exec argument injection in pull request merge | Critical | Same weakness, CWE-77 |
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