PHPUnit: Argument injection via newline in PHP INI values forwarded to child processes

Impact

PHPUnit forwards PHP INI settings to child processes (used for isolated/PHPT test execution) as -d name=value command-line arguments without neutralizing INI metacharacters. Because PHP's INI parser interprets " as a string delimiter, ; as the start of a comment, and most importantly a newline as a directive separator, a value containing a newline is parsed by the child process as multiple INI directives.

An attacker able to influence a single INI value can therefore inject arbitrary additional directives into the child's configuration, including auto_prepend_file, extension, disable_functions, open_basedir, and others. Setting auto_prepend_file to an attacker-controlled path yields remote code execution in the child process.

Sources of INI values that participate in the attack:

• <ini name="…" value="…"/> entries in phpunit.xml / phpunit.xml.dist
• INI settings inherited from the host PHP runtime via ini_get_all()

Threat Model

Exploitation requires the attacker to control the content of an INI value read by PHPUnit. In practice this means write access to the project's phpunit.xml, the host php.ini, or the PHP binary's environment. The most realistic exposure is Poisoned Pipeline Execution (PPE): a pull request from an untrusted contributor that modifies phpunit.xml to include a newline-containing INI value, executed by a CI system that runs PHPUnit against the PR without isolation. A malicious newline is not visibly distinguishable from a legitimate value in a typical diff review.

Affected Component

PHPUnit\Util\PHP\JobRunner::settingsToParameters()

Patches

The fix has two parts:

1. Reject line-break characters

Because a newline or carriage return in an INI value has no legitimate use and is the primitive that enables directive injection, any PHP setting value containing \n or \r is now rejected with an explicit PhpProcessException. This follows the same "visibility over silence" principle applied in CVE-2026-24765: the anomalous state fails loudly in CI output rather than being silently sanitized, giving operators an opportunity to investigate whether it reflects tampering, environment contamination, or an unexpected upstream change.

2. Quote remaining metacharacters

Values containing " or ;, both of which have legitimate uses (e.g., regex-valued INI settings such as ddtrace's datadog.appsec.obfuscation_parameter_value_regexp), are wrapped in double quotes with inner " escaped as \", so PHP's INI parser reads them as literal string contents rather than comment/delimiter tokens. Plain values are forwarded unchanged so that boolean keywords (On/Off) and bitwise expressions (E_ALL & ~E_NOTICE) retain their INI semantics.

Workarounds

If upgrading is not immediately possible:

1. Audit INI values: Ensure no <ini value="…"> entry in phpunit.xml / phpunit.xml.dist contains newline, ", or ; characters, and that nothing writes such values into configuration at build time.
2. Isolate CI execution of untrusted code: Run PHPUnit against pull requests only in ephemeral, containerized runners that discard filesystem state between jobs; require human review before executing PRs from forks; enforce branch protection on workflows that handle secrets (pull_request_target and similar). These mitigations apply to the broader PPE risk class and are effective against this vulnerability as well.
3. Restrict who can modify phpunit.xml: Treat phpunit.xml as security-sensitive in code review, particularly <ini> entries.
4. Sanitize host INI: Ensure the host PHP's php.ini does not contain values with embedded newlines or unescaped metacharacters.