CVE-2026-42549

The make:controller CLI command calls mkdir(..., recursive: true) on a path built from the user-supplied controller name, before Nette's class-name validation runs. The class-file write is correctly rejected by Nette when the name contains /, but the recursive directory creation side effect is already committed, including directories located outside the project root through ../ traversal.

Affected code

flight/commands/ControllerCommand.php (≈ 63-66):

if (is_dir(dirname($controllerPath)) === false) {
    $io->info('Creating directory ' . dirname($controllerPath), true);
    mkdir(dirname($controllerPath), 0755, true);   // un-normalized, runs before validation
}

Proof of concept

$ php vendor/flightphp/runway/runway make:controller '../../../../tmp/CONTROLLER_TRAVERSAL_TEST/pwn'
Creating directory .../app/controllers/../../../../tmp/CONTROLLER_TRAVERSAL_TEST
Nette\InvalidArgumentException: Value '../../../../tmp/CONTROLLER_TRAVERSAL_TEST/pwnController' is not valid class name.

$ ls /home/user/tmp/CONTROLLER_TRAVERSAL_TEST
(directory exists, created before the exception was thrown)

Patch (fixed in 3.18.1, commit b8dd23a)

The controller name is now normalized with basename() and validated against ^[A-Za-z_][A-Za-z0-9_]*$ before any mkdir side effect runs.

Credit

Discovered by @Rootingg.

• Arbitrary directory creation outside the project root, executable by any local actor that can run the Flight CLI (developer machine, shared CI build agent, compromised dev container).
• Primes log-file planting for chained LFI exploitation (e.g. creating a directory where an attacker can later drop a .php file to be included via a distinct template-include weakness).
• On Windows, the \ separator opens additional traversal surface.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-42549 has a CVSS score of 4.4 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.18.1); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-42549? CVE-2026-42549 is a medium-severity path traversal vulnerability in flightphp/core (composer), affecting versions < 3.18.1. It is fixed in 3.18.1. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-42549? CVE-2026-42549 has a CVSS score of 4.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of flightphp/core are affected by CVE-2026-42549? flightphp/core (composer) versions < 3.18.1 is affected.
4. Is there a fix for CVE-2026-42549? Yes. CVE-2026-42549 is fixed in 3.18.1. Upgrade to this version or later.
5. Is CVE-2026-42549 exploitable, and should I be worried? Whether CVE-2026-42549 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-42549 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-42549? Upgrade flightphp/core to 3.18.1 or later.