ISITDTU CTF 2023 Blog
Acknowledgement
First, I would like to express my deepest gratitude to NUS School of Computing for their SoC Take on the World (SToW) financial aid program which covered our plane ticket.
How I got in?
We were invited by the kind people from Duy Tan University after playing in their preliminary round. I didn’t actually play in that round as I think I was busy then, but my club was nice enough to give me a spot to compete in the finals.
My 4 other teammates and I took the night bus back to Malaysia and the morning plane from KLIA to Da Nang International Airport. The reason we took such a long trip was because this was the cheapest route.
Day before competition
After we landed at Da Nang International Airport, we were greeted by the driver that one of our teammates, Vinh, booked beforehand. Since it was already afternoon, we went for lunch at a nearby restaurant.
Then, we went to check in at our hotel and quickly took the car to a nearby beach (Pham Van Dong Beach).
The beach was really clean even though it is a tourist spot. I eventually took off my shoes to touch the seawater, which was nice until we had to find a place to wash our feet.
We stayed until the sun was about to set, which was planned with our next destination in mind. We hopped in the car and headed towards Chua Linh Ung (Pagoda Linh Ung).
We went in to take a look. Since my family practices Buddhism, I did a quick prayer and paid my respect before looking around the insides. No photos of the interior because I felt like it wasn’t appropriate to take any. When we went back outside, the sun was already almost set. Since the pagoda is on the side of a hill, facing the beach we were at just now, we got to see an amazing view.
This position of “sitting” on (the side of) the hill and facing the sea was said to be a blessing for the safety of the fishermen. As the sky became darker, spotlights were turned on to light up the statue of Guan Yin.
We took some more photos and a final walk around the place before going for dinner. For dinner, we had My Quang Tho (wide rice noodles with frog soup). It sounds scary but it’s quite nice.
This meal was also when we started to experience just how much fresh vegetables the Vietnamese eat. After dinner, we went back to the hotel for a quick briefing about the setup required for the competition. After that, we slept rather early since the CTF on the next day started very early.
CTF Day
I woke up at 6 or something, since we wanted to leave at 7 to catch breakfast and make it on time for the CTF at 7:45. For breakfast, we had the classic Pho, which was so, so, so delicious. We got to try out the condiments and sauces that were on the table and they all gave the soup a different twist. I especially liked the garlic & chilli pickle juice which was savory and spicy with a little tang.
We then went to the Duy Tan Building in Duy Tan University for the competition. They gave us “uniforms” and asked us to change into it before we started. Also, they apparently call CTF competitions “exams”, which I just find interesting. There were some snacks and drinks served. Not the best amongst on-site CTFs I’ve been to but it was still nice to have.
About the competition itself, it was an Attack-Defense (AD) style competition which I had minimal exposure to. Every team had their own server instance with the same services hosted on a LAN. Each team should analyze the services (programs) to find vulnerabilities and send attacks to all other teams to obtain the flag. While the attacks are going on, each team should also attempt to patch their programs to fix the vulnerabilities without faulting the service’s original intended functionality.
There were 4 services in total: 2 web and 2 pwn (binary exploitation). I worked on the 2 pwn challenges with another teammate, Lambang. The vulnerabilities were straightforward but the attacks were extremely sophisticated. We ended up patching the binaries very quickly to prevent others from attacking us, but the second service was still under attack.
Our attacks worked for the first pwn service before all teams patched the vulnerability. Meanwhile, even after patching the second service, teams were still able to attack us. On top of that, whenever we patch our service, if the behaviour of our program is no longer as intended, then our service is considered “down” and marks will be deducted. So we had to keep reverting our changes to stop the bleeding, whilst figuring out the correct patch.
Good thing we had 3 more experts working on the 2 web, which I think they did quite well, helping us maintain a good 6th place, the last slot for consolation prize.
For dinner, we went for a big feast.
Vinh also introduced us to their “drinking call”, though we were only drinking lemonade 
. We were the only group in that restaurant because we were too late for dinner, but he said that people will start calling if they hear a call from a nearby table, and it will spread like a virus.
After dinner, I suggested we grab dessert. I’ve been to Hanoi once and had that dessert which was so unforgettable, so I wanted to have it once again with everyone. It’s called Chè, and there was a famous shop called Chè Liên.
We ordered Chè Thái Sầu, which is this almost milky drink with jelly-like things inside and a big blob of durian flesh on it. I really don’t know what it is, so it’s pretty hard for me to describe . You are supposed to add the ice to the dessert to chill it down and dilute it a little. It was just phenomenal.
Afterwards, we went to see the fire show at the Dragon Bridge. The Dragon Bridge has a fire-spitting show on every Friday, Saturday and Sunday night at 9pm. It was very crowded, but we found a nice spot with a nice angle to view the fire.
It paused for several minutes after 3 bursts of fire and repeated that for 4 times. We thought it was over, but it started shooting water, which was way cooler in my opinion.
I ran into the water since I saw many others doing the same. The others followed me and we all got ourselves a little wet. After that, we went back to our hotel for a good night’s sleep.
Day after the competition
For our final day, we woke up a bit late since we were on our own schedule.
Lambang left in the morning, so it’s just the 4 of us left :(
We ordered Xôi (savoury sticky rice with a bunch of toppings) on Grab food, then walked to a nearby coffee shop to try their salty coffee.
Whilst waiting for our driver to come, we walked to the same beach we went to on day 1.
We soon returned to the hotel lobby a little before the driver arrived. We asked him to buy us Bánh mì on his way here, so we had that before hopping in the car to our first spot to visit.
Marble Hills
Our first spot of the day is Marble Hills. The cave was slightly slippery and the stairs were super steep. It was also nice having Vinh to explain things to us along the way.
After the cave, we took the elevator to the hills. The whole journey was like half cave exploration and half mountain hiking.
There are 5 hills, and we went up the highest one to catch the amazing view.
We rested for some time and headed back down to the pagoda there. It is also called Chuah Linh Ung, and also has the characteristic position of sitting on a hill and facing the sea.
Hội An
Our second (and also last) spot of the day is Hội An. It’s an hour’s drive away from Marble Hills, so it was already nighttime when we arrived. This was also planned, as Hội An is about the night street view.
We first resolved our hunger issues from the intense physical activities we had. We went for the Hội An special “Vietnamese chicken rice”, Cơm Gà.
After filling our tummies, we went for the boat ride that we saw earlier.
It was a nice 20-minute boat ride with the guide telling us some history of the place. (Thanks Vinh for the helpful translations)
We took a small walk around to possibly buy some souvenirs. Then, before we left, we went to buy this mysterious drink that Vinh said makes people want to go to the toilet. It didn’t really have an effect on us, but it was super tasty, especially after a long walk around.
And that concludes our trip!
Final words
This trip to Vietnam made me appreciate Vietnamese food and Vietnamese culture. The CTF challenges were very difficult but I still learned something here and there nonetheless. It was also very nice getting to know some new people from different countries.
Special thanks to Vinh for taking care of us 4 non-Vietnamese speakers and making sure the tour went smoothly. (vãi lồn 
)