overview.md (6478B)
1 --- 2 title: "88tcp/udp - Pentesting Kerberos" 3 section: "Network Services" 4 sectionSlug: "network-services-pentesting" 5 sourcePath: "src/network-services-pentesting/pentesting-kerberos-88/README.md" 6 sourceUrl: "https://github.com/HackTricks-wiki/hacktricks/blob/188de82beb54e70956b2952367a0af91d26758b8/src/network-services-pentesting/pentesting-kerberos-88/README.md" 7 sha: "188de82beb54e70956b2952367a0af91d26758b8" 8 isIndex: true 9 modified: true 10 license: "CC-BY-NC-4.0" 11 --- 12 13 # 88tcp/udp - Pentesting Kerberos 14 15 ## Basic Information 16 17 **Kerberos** is a network authentication protocol: it establishes identities and session keys, while each application service makes its own authorization decision about the authenticated principal.<sup>[[5]](#references)</sup> 18 19 In environments like **Active Directory**, **Kerberos** is instrumental in establishing the identity of users by validating their secret passwords. This process ensures that each user's identity is confirmed before they interact with network resources. However, **Kerberos** does not extend its functionality to evaluate or enforce the permissions a user has over specific resources or services. Instead, it provides a secure way of authenticating users, which is a critical first step in the security process. 20 21 After Kerberos authentication, the target service evaluates the user's rights and permissions using its local policy and any authorization data carried in the ticket. This separates authentication from application-specific access control.<sup>[[5]](#references)</sup> 22 23 **Default Port:** 88/tcp/udp 24 25 ```text 26 PORT STATE SERVICE 27 88/tcp open kerberos-sec 28 ``` 29 30 ### **To learn how to abuse Kerberos you should read the post about** [**Active Directory**](../../windows-hardening/active-directory-methodology/index.html)**.** 31 32 ## Kerberos-only environments: client prep and troubleshooting 33 34 When NTLM is disabled on domain services (SMB/WinRM/etc.), you must authenticate with Kerberos. Common pitfalls and a working workflow:<sup>[[4]](#references)</sup> 35 36 - Time synchronization is mandatory. If your host clock is skewed by more than a few minutes you will see `KRB_AP_ERR_SKEW` and all Kerberos auth will fail. Sync against the DC: 37 38 ```bash 39 # quick one-shot sync (requires sudo) 40 sudo ntpdate <dc.fqdn> || sudo chronyd -q 'server <dc.fqdn> iburst' 41 ``` 42 43 - Generate a valid krb5.conf for the target realm/domain. `netexec` (CME fork) can output one for you while testing SMB:<sup>[[1]](#references)</sup> 44 45 ```bash 46 # Generate krb5.conf and install it 47 netexec smb <dc.fqdn> -u <user> -p '<pass>' -k --generate-krb5-file krb5.conf 48 sudo cp krb5.conf /etc/krb5.conf 49 ``` 50 51 - Obtain a TGT and verify the ccache:<sup>[[3]](#references)</sup> 52 53 ```bash 54 kinit <user> 55 klist 56 ``` 57 58 - Use Kerberos with SMB tooling (no passwords sent, uses your ccache): 59 60 ```bash 61 # netexec / CME 62 netexec smb <dc.fqdn> -k # lists shares, runs modules using Kerberos 63 # impacket examples also support -k / --no-pass to use the ccache 64 smbclient --kerberos //<dc.fqdn>/IPC$ 65 ``` 66 67 - GSSAPI SSH single sign-on (OpenSSH to Windows OpenSSH server):<sup>[[2]](#references)</sup> 68 69 ```bash 70 # Ensure krb5.conf is correct and you have a TGT (kinit) 71 # Use the FQDN that matches the host SPN. Wrong names cause: "Server not found in Kerberos database" 72 ssh -o GSSAPIAuthentication=yes <user>@<host.fqdn> 73 ``` 74 75 Tips: 76 - Ensure your `/etc/hosts` resolves the exact FQDN you will SSH/SMB to, and that it comes before any bare domain entries if you are overriding DNS. SPN mismatches break GSSAPI. 77 - If NTLM is disabled on SMB you may see `STATUS_NOT_SUPPORTED` with NTLM attempts; add `-k` to force Kerberos. 78 79 ## More 80 81 ### Shodan 82 83 - `port:88 kerberos` 84 85 ### MS14-068 86 87 MS14-068 allowed a domain user to forge authorization data in a Kerberos ticket and have a vulnerable Domain Controller accept elevated group membership, potentially yielding Domain Admin privileges.<sup>[[6]](#references)</sup> 88 89 The `pykek` exploit is archived in the SecWiki Windows kernel exploits collection.<sup>[[7]](#references)</sup> 90 91 ## HackTricks Automatic Commands 92 93 ```text 94 Protocol_Name: Kerberos #Protocol Abbreviation if there is one. 95 Port_Number: 88 #Comma separated if there is more than one. 96 Protocol_Description: AD Domain Authentication #Protocol Abbreviation Spelled out 97 98 Entry_1: 99 Name: Notes 100 Description: Notes for Kerberos 101 Note: | 102 Kerberos operates on a principle where it authenticates users without directly managing their access to resources. This is an important distinction because it underlines the protocol's role in security frameworks. 103 In environments like **Active Directory**, Kerberos is instrumental in establishing the identity of users by validating their secret passwords. This process ensures that each user's identity is confirmed before they interact with network resources. However, Kerberos does not extend its functionality to evaluate or enforce the permissions a user has over specific resources or services. Instead, it provides a secure way of authenticating users, which is a critical first step in the security process. 104 105 https://book.hacktricks.wiki/en/network-services-pentesting/pentesting-kerberos-88/index.html 106 107 Entry_2: 108 Name: Pre-Creds 109 Description: Brute Force to get Usernames 110 Command: nmap -p 88 --script=krb5-enum-users --script-args krb5-enum-users.realm="{Domain_Name}",userdb={Big_Userlist} {IP} 111 112 Entry_3: 113 Name: With Usernames 114 Description: Brute Force with Usernames and Passwords 115 Note: consider git clone https://github.com/ropnop/kerbrute.git ./kerbrute -h 116 117 Entry_4: 118 Name: With Creds 119 Description: Attempt to get a list of user service principal names 120 Command: GetUserSPNs.py -request -dc-ip {IP} active.htb/svc_tgs 121 ``` 122 123 ## References 124 125 - [1] [NetExec (CME) wiki – Kerberos and krb5.conf generation](https://www.netexec.wiki/) 126 - [2] [OpenSSH GSSAPIAuthentication](https://man.openbsd.org/ssh_config#GSSAPIAuthentication) 127 - [3] [MIT Kerberos Documentation – For users (ticket management: kinit/klist)](https://web.mit.edu/kerberos/krb5-1.22/doc/user/index.html) 128 - [4] [0xdf – HTB: TheFrizz](https://0xdf.gitlab.io/2025/08/23/htb-thefrizz.html) 129 - [5] [MIT Kerberos - Host configuration and login authorization](https://web.mit.edu/kerberos/krb5-latest/doc/admin/host_config.html) 130 - [6] [ADSecurity - MS14-068 Kerberos vulnerability](https://adsecurity.org/?p=541) 131 - [7] [SecWiki - MS14-068 `pykek`](https://github.com/SecWiki/windows-kernel-exploits/tree/master/MS14-068/pykek)