Pheditor: Terminal command-allowlist bypass via argument injection leads to RCE — surviving vector after the metacharacter-sanitization fixes

Summary

pheditor's terminal feature restricts callers to an allowlist of commands (TERMINAL_COMMANDS) and rejects shell metacharacters. The allowlist is enforced as a PREFIX match with no argument validation, and the allowlist includes binaries that grant arbitrary command execution through their own options (find, git, php, tar, grep). A caller can therefore run any command using only allowlisted binaries and no rejected metacharacter, escaping the allowlist restriction the terminal feature relies on.

Relationship to the prior terminal advisories (this is a surviving, distinct vector)

The prior terminal advisories were all shell-metacharacter injections: GHSA-9643-6xjp-vx57 ($()), GHSA-wg4w-wr5q-6vjc (|, backtick, newline), GHSA-jvc5-58fv-w8cq (; via the dir field). The current code rejects those characters. This report is a different class — CWE-88 argument injection through an allowlisted binary's flags — which the metacharacter denylist does not address.

Root cause (HEAD, v2.0.6)

In the terminal action handler of pheditor.php:

1. :588 rejects &, ;, |, $, backtick, \n, \r. It does NOT reject space, -, {, }, +, /, ..
2. :595-605 checks the command against TERMINAL_COMMANDS (defined :25: ls,...,php,...,git,find,grep,...,tar,...,composer,exit) using a PREFIX match: strlen($command) >= strlen($value) && substr($command, 0, strlen($value)) == $value. There is no word boundary and no validation of the arguments that follow.
3. :617 runs the command through the shell unchanged: shell_exec((empty($dir) ? null : 'cd ' . escapeshellarg($dir) . ' && ') . $command . ' && echo \ ; pwd').

So a command beginning with an allowlisted binary, carrying a code-exec flag, and containing none of the rejected characters reaches shell_exec intact.

Proof of concept (reproduced)

POST to the terminal action with: command = find . -maxdepth 0 -exec touch /tmp/PWNED {} + dir = (any)

This contains no rejected metacharacter, prefix-matches the allowlisted find, and find -exec runs an arbitrary program. A faithful harness mirroring the three guards (poc/reproduction.sh, poc/transcript.txt) creates the marker file. Other allowlisted-binary payloads with the same property: git -c alias.x='!touch /tmp/PWNED' x, php -r 'system("id");', tar -cf /dev/null --checkpoint=1 --checkpoint-action=exec="touch /tmp/PWNED" ..

Impact

Arbitrary command execution on the host, under the web server's privileges, for a caller with the terminal permission (enabled in the default configuration). The exposure is amplified by GHSA-p4h7-p9rj-2pq2 (hardcoded default admin password with no forced change): a default deployment grants the authenticated access needed to reach the terminal action with a single known credential, making the chain effectively unauthenticated RCE.

Remediation

Validate the FULL command, not just its prefix: tokenize and require the program to be an allowlisted binary AND constrain its arguments (reject -exec/-execdir for find, -c/--upload-pack for git, -r/-d for php, --checkpoint-action/--to-command for tar, -f/--file program forms, etc.), or run each command as an argv array through a restricted launcher with no shell, or remove the code-exec-capable binaries from the allowlist. A prefix allowlist over a shell sink cannot constrain capability.

Credit: anir0y (independent security research).