CVE-2026-28508

Idno is a social publishing platform. Prior to version 1.6.4, a logic error in the API authentication flow causes the CSRF protection on the URL unfurl service endpoint to be trivially bypassed by any unauthenticated remote attacker. Combined with the absence of a login requirement on the endpoint itself, this allows an attacker to force the server to make arbitrary outbound HTTP requests to any host, including internal network addresses and cloud instance metadata services, and retrieve the response content. This issue has been patched in version 1.6.4.

Idno is a social publishing platform. Prior to version 1.6.4, a logic error in the API authentication flow causes the CSRF protection on the URL unfurl service endpoint to be trivially bypassed by any unauthenticated remote attacker. Combined with the absence of a login requirement on the endpoint itself, this allows an attacker to force the server to make arbitrary outbound HTTP requests to any host, including internal network addresses and cloud instance metadata services, and retrieve the response content. This issue has been patched in version 1.6.4.

Summary

A logic error in the API authentication flow causes the CSRF protection on the URL unfurl service endpoint to be trivially bypassed by any unauthenticated remote attacker. Combined with the absence of a login requirement on the endpoint itself, this allows an attacker to force the server to make arbitrary outbound HTTP requests to any host, including internal network addresses and cloud instance metadata services, and retrieve the response content.

Component: Idno/Pages/Service/Web/UrlUnfurl.php, Idno/Core/Session.php, Idno/Core/Actions.php
Vulnerability Class: Server-Side Request Forgery (SSRF) Authentication Required: None
CVSSv4 Base Score: 9.2 (High) - AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N Affected Endpoint: GET /service/web/unfurl?url=<attacker-controlled-url> Handled by Idno\Pages\Service\Web\UrlUnfurl::getContent(). Affected Versions: <= 1.6.3

cat version.idno
version = '1.6.3'
build = 2026021301

Code Flow

Step 1 — Endpoint access control

UrlUnfurl::getContent() (UrlUnfurl.php:36) enforces two access controls:
$this->xhrGatekeeper(); $this->tokenGatekeeper();

Notably, the original authentication check ($this->gatekeeper()) was explicitly removed with the following comment left in the source:

//$this->gatekeeper(); // Gatekeeper to ensure this service isn't abused by third parties
// UPDATE: Needs to be accessible to logged out users, TODO, find a way to prevent abuse

This leaves the endpoint accessible to unauthenticated users, with only the two remaining gatekeepers as a barrier.

Step 2 — Bypassing xhrGatekeeper()

Page::xhrGatekeeper() (Page.php:876) checks whether the request was made with the X-Requested-With: XMLHttpRequest header:

function xhrGatekeeper()
{
    if (!$this->xhr) {
        $this->deniedContent();
    }
}

This check is trivially bypassed by any HTTP client capable of setting custom headers.

Step 3 — Bypassing tokenGatekeeper() via premature API flag

Page::tokenGatekeeper() (Page.php:887) calls Actions::validateToken():

function tokenGatekeeper()
{
    $url = $this->currentUrl();
    $bits = explode('?', $url);
    $url = $bits[0];
    if (!\Idno\Core\Idno::site()->actions()->validateToken($url, false)) {
        $this->deniedContent();
    }
}

Actions::validateToken() (Actions.php:23) short-circuits entirely when isAPIRequest() returns true:

public static function validateToken($action = '', $haltExecutionOnBadRequest = true)
{
    if (Idno::site()->session()->isAPIRequest()) {
        return true;
    }
    return parent::validateToken($action, $haltExecutionOnBadRequest);
}

isAPIRequest() reads the is_api_request flag from the session:

function isAPIRequest()
{
    if (!empty($_SESSION['is_api_request'])) {
        return true;
    }
    return false;
}

The flag is set in Session::tryAuthUser() (Session.php:488), which runs early in the request lifecycle. The critical defect is here:

$apiUsername  = $_SERVER['HTTP_X_IDNO_USERNAME']  ?? $_SERVER['HTTP_X_KNOWN_USERNAME']  ?? null;
$apiSignature = $_SERVER['HTTP_X_IDNO_SIGNATURE'] ?? $_SERVER['HTTP_X_KNOWN_SIGNATURE'] ?? null;
if (!$return && !empty($apiUsername) && !empty($apiSignature)) {
    $this->setIsAPIRequest(true);   // ← flag set here, before any credential check
    $user = \Idno\Entities\User::getByHandle($apiUsername);
    if (!empty($user)) {
        $compare_hmac = base64_encode(hash_hmac('sha256', $_SERVER['REQUEST_URI'], $key, true));
        if ($hmac == $compare_hmac) {       // ← HMAC verified here, too late
            $return = $this->refreshSessionUser($user);
        }
    }
}

setIsAPIRequest(true) is called unconditionally as soon as both X-IDNO-USERNAME and…

Idno is a social publishing platform. Prior to version 1.6.4, a logic error in the API authentication flow causes the CSRF protection on the URL unfurl service endpoint to be trivially bypassed by any unauthenticated remote attacker. Combined with the absence of a login requirement on the endpoint itself, this allows an attacker to force the server to make arbitrary outbound HTTP requests to any host, including internal network addresses and cloud instance metadata services, and retrieve the response content. This issue has been patched in version 1.6.4.

Idno is a social publishing platform. Prior to version 1.6.4, a logic error in the API authentication flow causes the CSRF protection on the URL unfurl service endpoint to be trivially bypassed by any unauthenticated remote attacker. Combined with the absence of a login requirement on the endpoint itself, this allows an attacker to force the server to make arbitrary outbound HTTP requests to any host, including internal network addresses and cloud instance metadata services, and retrieve the response content. This issue has been patched in version 1.6.4.

Summary

A logic error in the API authentication flow causes the CSRF protection on the URL unfurl service endpoint to be trivially bypassed by any unauthenticated remote attacker. Combined with the absence of a login requirement on the endpoint itself, this allows an attacker to force the server to make arbitrary outbound HTTP requests to any host, including internal network addresses and cloud instance metadata services, and retrieve the response content.

Component: Idno/Pages/Service/Web/UrlUnfurl.php, Idno/Core/Session.php, Idno/Core/Actions.php
Vulnerability Class: Server-Side Request Forgery (SSRF) Authentication Required: None
CVSSv4 Base Score: 9.2 (High) - AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N Affected Endpoint: GET /service/web/unfurl?url=<attacker-controlled-url> Handled by Idno\Pages\Service\Web\UrlUnfurl::getContent(). Affected Versions: <= 1.6.3

cat version.idno
version = '1.6.3'
build = 2026021301

Code Flow

Step 1 — Endpoint access control

UrlUnfurl::getContent() (UrlUnfurl.php:36) enforces two access controls:
$this->xhrGatekeeper(); $this->tokenGatekeeper();

Notably, the original authentication check ($this->gatekeeper()) was explicitly removed with the following comment left in the source:

//$this->gatekeeper(); // Gatekeeper to ensure this service isn't abused by third parties
// UPDATE: Needs to be accessible to logged out users, TODO, find a way to prevent abuse

This leaves the endpoint accessible to unauthenticated users, with only the two remaining gatekeepers as a barrier.

Step 2 — Bypassing xhrGatekeeper()

Page::xhrGatekeeper() (Page.php:876) checks whether the request was made with the X-Requested-With: XMLHttpRequest header:

function xhrGatekeeper()
{
    if (!$this->xhr) {
        $this->deniedContent();
    }
}

This check is trivially bypassed by any HTTP client capable of setting custom headers.

Step 3 — Bypassing tokenGatekeeper() via premature API flag

Page::tokenGatekeeper() (Page.php:887) calls Actions::validateToken():

function tokenGatekeeper()
{
    $url = $this->currentUrl();
    $bits = explode('?', $url);
    $url = $bits[0];
    if (!\Idno\Core\Idno::site()->actions()->validateToken($url, false)) {
        $this->deniedContent();
    }
}

Actions::validateToken() (Actions.php:23) short-circuits entirely when isAPIRequest() returns true:

public static function validateToken($action = '', $haltExecutionOnBadRequest = true)
{
    if (Idno::site()->session()->isAPIRequest()) {
        return true;
    }
    return parent::validateToken($action, $haltExecutionOnBadRequest);
}

isAPIRequest() reads the is_api_request flag from the session:

function isAPIRequest()
{
    if (!empty($_SESSION['is_api_request'])) {
        return true;
    }
    return false;
}

The flag is set in Session::tryAuthUser() (Session.php:488), which runs early in the request lifecycle. The critical defect is here:

$apiUsername  = $_SERVER['HTTP_X_IDNO_USERNAME']  ?? $_SERVER['HTTP_X_KNOWN_USERNAME']  ?? null;
$apiSignature = $_SERVER['HTTP_X_IDNO_SIGNATURE'] ?? $_SERVER['HTTP_X_KNOWN_SIGNATURE'] ?? null;
if (!$return && !empty($apiUsername) && !empty($apiSignature)) {
    $this->setIsAPIRequest(true);   // ← flag set here, before any credential check
    $user = \Idno\Entities\User::getByHandle($apiUsername);
    if (!empty($user)) {
        $compare_hmac = base64_encode(hash_hmac('sha256', $_SERVER['REQUEST_URI'], $key, true));
        if ($hmac == $compare_hmac) {       // ← HMAC verified here, too late
            $return = $this->refreshSessionUser($user);
        }
    }
}

setIsAPIRequest(true) is called unconditionally as soon as both X-IDNO-USERNAME and…