Front Door Access: Why Identity Attacks Trump Zero-Days
I just caught the latest report on Hacker News discussing how attackers are increasingly bypassing complex exploit chains in favor of simple identity-based attacks. It’s a stark reminder that while we're all chasing down supply chain CVEs and patching kernel zero-days, the most reliable initial access vector remains a valid set of credentials.
We’re seeing a massive resurgence in credential stuffing and brute-forcing, particularly targeting protocols that don’t support modern MFA (like legacy SMTP or basic auth). The attackers aren't exploiting a bug in the code; they're exploiting the trust we place in the user identity.
If you aren't monitoring for Impossible Travel or sudden bursts of failed authentication attempts, you're flying blind. For those using Microsoft Sentinel, here’s a decent KQL query to hunt for potential credential stuffing patterns targeting your Entra ID tenants:
SigninLogs
| where ResultType == "50126" // Invalid username or password
| summarize Count = count() by IPAddress, UserPrincipalName, bin(TimeGenerated, 5m)
| where Count > 5 // Threshold for stuffing attempts
| join kind=inner (SigninLogs | where ResultType == "0" // Success
| project SuccessTime=TimeGenerated, UserPrincipalName, IPAddress) on UserPrincipalName
| project-away UserPrincipalName1
| where SuccessTime > TimeGenerated + 5m
This looks for IPs failing multiple times against a user, then that same user successfully logging in from a different IP shortly after. It’s a classic pattern.
Given the ease of buying valid creds on the dark web, how are you all handling legacy auth protocols? Are you strictly blocking them, or have you found a way to force MFA on them?
Legacy auth is the bane of my existence. We finally killed Basic Auth for Exchange last year, and our 'failed login' telemetry dropped by nearly 60%. It was all noise from password spraying tools. For on-prem AD, I recommend checking for Event ID 4776 (Credential Validation) failures. If you see a source computer authenticating as multiple different users quickly, that's usually a Kerbrute or spray attempt:
Get-WinEvent -FilterHashtable @{LogName='Security'; ID=4776} | Where-Object {$_.Message -match '0xc000006a'} | Select-Object TimeCreated, Message
It's funny, during our last red team engagement, they spent zero days trying to exploit a web vulnerability. They just phished a junior dev's GitHub token, cloned a repo, and found a hardcoded DB connection string in a comment. It was game over in 20 minutes. No 'exploit' needed. We've since moved to enforce branch protection rules and secret scanning, but it proves your point: Identity and OpSec failures are easier to leverage than memory corruption bugs.
Visibility is the real challenge here. We implemented risk-based Conditional Access policies, but auditing legacy authentication usage was the game changer. I run this simple KQL query weekly to spot brute-force spikes on protocols like IMAP or POP3 before they become a breach.
AADNonInteractiveUserSignInLogs
| where ResultType == "50126"
| summarize FailedAttempts = count() by AppDisplayName, bin(TimeGenerated, 1h)
| where FailedAttempts > 50
Absolutely. While we obsess over MFA, service accounts often fly under the radar. They typically use static passwords and bypass MFA, making them prime targets for credential stuffing. I recommend regularly auditing for stale or over-privileged accounts.
Here is a quick PowerShell snippet to find enabled accounts with passwords set to never expire:
Get-ADUser -Filter {Enabled -eq $true -and PasswordNeverExpires -eq $true} -Properties LastLogonDate | Where-Object { $_.LastLogonDate -lt (Get-Date).AddDays(-90) } | Select-Object Name, LastLogonDate
Trimming these down forces attackers to look elsewhere.
While everyone talks about MFA, don't overlook Smart Lockout policies to mitigate brute-force effectively. We configured our tenant to lock accounts for 10 minutes after 5 failed attempts, which drastically reduces the success rate of password spraying. You can verify your current lockout settings via Graph API or the portal, but for a quick PowerShell check on your enforcement status:
Get-MsolPolicy -PolicyType Lockout | Select-Object Name, Definition
It’s a simple configuration that stops automated scripts in their tracks before they find a valid credential.
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