GHSA-wg4w-wr5q-6vjc Pheditor: Incomplete command sanitization in terminal feature allows RCE via pipe operator, backtick substitution, and newline injection
SummaryThe 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 `$` to the blocklist), the characters `|` (single pipe), `` ` `` (backtick), and the newline byte (`0x0A`) remain unblocked. An authenticated user with the `terminal` permission (enabled by default) can leverage any of these to bypass the `TERMINAL_COMMANDS` allowlist and execute arbitrary OS commands as the web server user.DetailsTested repository: https://github.com/pheditor/pheditorTested commit: `e538f05b6faec99e5b23726bc9c17d6b57774297` (current HEAD on `main`)Affected version: Pheditor 2.0.1+The terminal handler receives `$_POST['command']` and passes it to `shell_exec()` at `pheditor.php:586`:The blocklist at `pheditor.php:557` checks for `&`, `;`, `||`, and `$`, but does not block `|`, `` ` ``, or newline (`0x0A`):The `TERMINAL_COMMANDS` prefix check at `pheditor.php:566-573` only validates that the command starts with an allowed name. All three bypasses start with a whitelisted command prefix.**Bypass 1 — Single pipe `|`:**
The filter checks for `||` but not single `|`. Payload `ls | id` passes both the blocklist and the whitelist (starts with `ls`). The shell executes: `cd '<dir>' && ls | id && echo \ ; pwd`, running `id`.**Bypass 2 — Backtick `` ` ``:**
Backtick is not in the blocklist. Payload `` echo `id` `` passes the blocklist and whitelist (starts with `echo`). The shell executes `id` inside backtick substitution.**Bypass 3 — Newline `0x0A`:**
A literal newline byte is not in the blocklist. Payload `ls\ntouch /tmp/proof` (where `\n` is 0x0A) passes both checks. Only the first line is validated against the whitelist. The second line runs as an independent command.PoC**Environment:** Any system running PHP 8.x with pheditor.php deployed and `shell_exec()` enabled.**Setup:****Authenticate** (default password `admin`):**Bypass 1 (pipe `|`):**Expected: `{"error":false,"message":"OK","result":"uid=... gid=...\n",...}` — `id` output proves RCE.**Bypass 2 (backtick):**Expected: Same `id` output in response.**Bypass 3 (newline 0x0A):**Expected: Same `id` output in response.**Control (blocked command without bypass):**Expected: `{"error":true,"message":"Command not allowed..."}` — allowlist enforced.**Cleanup:**ImpactOS Command Injection (CWE-78). Any authenticated Pheditor user with the `terminal` permission (enabled by default) can bypass the `TERMINAL_COMMANDS` allowlist and execute arbitrary OS commands as the web server user. This is a bypass of the partial fix for GHSA-9643-6xjp-vx57 — that fix addressed `$()` substitution but three additional shell metacharacters remain unblocked.**Attacker privileges:** Authenticated user (PR:L). Combined with default password `admin`, effectively PR:N.**Impact:** Full read/write/execute access as the web server user. Confidentiality: High (read any accessible file). Integrity: High (write/delete files, deploy webshells). Availability: High (disrupt services).**Suggested remediation:** Parse the command into executable + arguments, validate the executable against `TERMINAL_COMMANDS` with exact match, pass each argument through `escapeshellarg()`, or use `proc_open()` with an argument array to avoid shell interpretation entirely.
CVSS v3.1 score: 8.8