When working with multi-forest Active Directory environments, LDAP binds across trust boundaries often present unexpected challenges. The error code 80090308: LdapErr: DSID-0C09030B, comment: AcceptSecurityContext error, data 525 specifically indicates a user object lookup failure in the target domain.

Contrary to common belief, being part of AUTHENTICATED USERS doesn't guarantee LDAP bind rights across all trust configurations. These permissions are critical:

1. Read permissions on the user object in the target domain
2. Allow access to this computer from the network (Security Policy)
3. Trusted for Delegation setting on domain controllers
4. Proper name suffix routing configuration

The discrepancy between REMOTE and FARAWAY domains typically stems from these areas:

nltest /server:DC_FARAWAY /trusted_domains
repadmin /showtrust /verbose

Here's a PowerShell script to verify and correct the common permission issues:

# Check effective permissions on target user object
$UserDN = "CN=myaccount,CN=Users,DC=FARAWAY,DC=com"
$Principal = "MAIN\myaccount"
$AuthType = [System.DirectoryServices.AuthenticationTypes]::Secure

$entry = New-Object DirectoryServices.DirectoryEntry(
    "LDAP://DC_FARAWAY/$UserDN",
    $Principal,
    $Password,
    $AuthType)

if ($entry.Name -eq $null) {
    $errorMsg = $Error[0].Exception.InnerException.Message
    Write-Host "Bind failure: $errorMsg"
    
    # Verify name resolution
    $context = New-Object System.DirectoryServices.ActiveDirectory.DirectoryContext(
        'DirectoryServer',
        'DC_FARAWAY',
        $Principal,
        $Password)
    
    try {
        $dc = [System.DirectoryServices.ActiveDirectory.DomainController]::GetDomainController($context)
        Write-Host "Successful direct authentication to DC"
    }
    catch {
        Write-Host "Underlying trust issue detected"
    }
}

For cross-forest scenarios, these additional settings are often needed:

• SID filtering exceptions for selective authentication
• DNS conditional forwarders for name resolution
• Firewall rules allowing Kerberos traffic (TCP/UDP 88)
• Service Principal Name (SPN) verification

When facing Data 525 errors, follow this diagnostic path:

1. Verify trust status with nltest
2. Check security descriptors with dsacls
3. Examine cross-domain object visibility
4. Test with explicit credentials rather than trust-based auth

When performing LDAP binds to Active Directory, these are the critical permissions required:

• "Authenticated Users" membership - By default, this group has "Allow access" permission in the domain controller's security policy
• Read permissions on the user object in AD
• Traverse/List permissions on the directory path to the user object

For cross-domain binds (especially across forest trusts), additional factors come into play:

// Example LDAP bind code showing proper authentication context
LDAPConnection ldapConnection = new LDAPConnection("ldap://FARAWAY.domain.com:389");
ldapConnection.AuthType = AuthType.Negotiate;
ldapConnection.Credential = new NetworkCredential(
    "MAIN\\myaccount", 
    "password", 
    "MAIN.domain.com");
try {
    ldapConnection.Bind();
} catch (LdapException ex) {
    // Handle error 525 specifically
    if (ex.ErrorCode == 525) {
        // Permission or account mapping issue
    }
}

The specific error 525 ("user not found") typically indicates:

1. The user account isn't properly mapped across the trust
2. Name resolution issues preventing the remote DC from locating the account
3. SID filtering is blocking the authentication attempt

Check these trust settings using PowerShell:

# Check trust direction and status
Get-ADTrust -Identity "FARAWAY" | 
    Select-Object Name,Direction,TrustType,TrustAttributes

# Verify SID filtering settings
(Get-ADTrust -Identity "FARAWAY").TrustAttributes -band 0x1

Enable extended logging to capture detailed authentication flow:

# Enable LDAP diagnostics in registry
New-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\NTDS\Diagnostics" 
    -Name "16 LDAP Interface Events" 
    -Value 2 
    -PropertyType DWORD

Check Event Viewer logs on both domain controllers for detailed error information about the failed bind attempt.

• Ensure DNS resolution works bidirectionally between forests
• Verify that "MAIN\myaccount" exists in the tokenGroups attribute on FARAWAY domain controllers
• Check if any IPsec policies might be interfering with authentication traffic