GHSA-wg4w-wr5q-6vjc: Pheditor: Incomplete command sanitization in terminal feature allows RCE via pipe operator, backtick substitution, and newline injection

Summary The terminal feature in Pheditor uses an incomplete character blocklist to sanitize user-supplied commands before passing them to shell_exec(). After the fix for GHSA-9643-6xjp-vx57 (which added $ to the blocklist), the characters | (single pipe), (backtick), and the newline byte (0x0A) remain unblocked. An authenticated user with the terminal permission (enabled by default) can leverage any of these to bypass the TERMINAL_COMMANDS` allowlist and execute arbitrary OS commands as the web server user. Details Tested repository: https://github.com/pheditor/pheditor Tested commit: e538f05b6faec99e5b23726bc9c17d6b57774297 (current HEAD on main) Affected version: Pheditor 2.0.1+ The terminal handler receives $_POST['command'] and passes it to shell_exec() at pheditor.php:586: $output = shell_exec((empty($dir) ? null : 'cd ' . escapeshellarg($dir) . ' && ') . $command . ' && echo \ ; pwd'); The blocklist at pheditor.php:557 checks for &, ;, ||, and $, but does not block |, , or newline (0x0A`): if (strpos($command, '&') !== false || strpos($command, ';') !== false || strpos($command, '||') !== false || strpos($command, '$') !== false) { echo json_error("Illegal character(s) in command (& ; ||)\n"); exit; } The TERMINAL_COMMANDS prefix check at pheditor.php:566-573 only validates that the command starts with an allowed name. All three bypasses start with a whitelisted command prefix. Bypass 1 — Single pipe |: The filter checks for || but not single |. Payload ls | id passes both the blocklist and the whitelist (starts with ls). The shell executes: cd '<dir>' && ls | id && echo \ ; pwd, running id. Bypass 2 — Backtick `: Backtick is not in the blocklist. Payload echo id passes the blocklist and whitelist (starts with echo). The shell executes id inside backtick substitution. Bypass 3 — Newline 0x0A: A literal newline byte is not in the blocklist. Payload ls\ntouch /tmp/proof (where \n is 0x0A) passes both checks. Only the first line is validated against