> For the complete documentation index, see [llms.txt](https://kabinet.gitbook.io/ctf-writeup/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://kabinet.gitbook.io/ctf-writeup/2025/defcon-cloud-village-2025/incident-responder.md).
# Incident Responder
{% file src="/files/xSwTZ09RAJhl6w6g9153" %}
Since we know the final attack chain was lambda function that encrypts stuff, lets try from the last step.
Grepping for encrypt, we can see that it encrypts the s3://hexnovadatabreach-databreach-content-dolphin/ImportantInformation.txt as well as the dynamodb/HevNovaDataBreachDynamoDB-databreach.
We are also given the API gateway URL for the lambda function
```
https://x7ia63zopb.execute-api.us-west-2.amazonaws.com
```
Trying to POST the the prod stage give us a 404 not found error
Playing around with the route, we managed to get a response out of the API Gateway.
```
curl -XGET https://x7ia63zopb.execute-api.us-west-2.amazonaws.com/decrypt/s3/hexnovadatabreach-databreach-content-dolphin/ImportantInformation.txt
```
It returns the encrypted important information.txt Doign a quick google, the gAAAA encryption is fernet encryption.
Looking at the CloudWatch log, we managed to find the encryption key.
Wrtiting a quick solve script we are able to get part1 of the flag.
```
import json
from cryptography.fernet import Fernet
# Fernet key from your input
fernet_key = "rFebkqIbEugh4uxwzR1HS49ICeE29fH-Rb7Ryk2exQA="
f = Fernet(fernet_key)
current = "gAAAA[truncated]"
while True:
try:
current = f.decrypt(current)
except Exception:
print(current)
break
```
For Part2, the flag is in the dynamodb.
{% code overflow="wrap" %}
```
curl -X GET https://x7ia63zopb.execute-api.us-west-2.amazonaws.com/decrypt/dynamodb/HevNovaDataBreachDynamoDB-databreach > output.json
```
{% endcode %}
I used LLM to write another solve script to parse the output and get the flag.
```python
import json
from cryptography.fernet import Fernet
# Fernet key from your input
fernet_key = "rFebkqIbEugh4uxwzR1HS49ICeE29fH-Rb7Ryk2exQA="
f = Fernet(fernet_key)
# Path to your JSON file
json_file = "output.json"
# Load the JSON
with open(json_file, "r") as f_in:
data = json.load(f_in)
for idx, item in enumerate(data.get("items", []), start=1):
try:
data_val = item["Data"]["S"]
key_val = item["DefCon33PartitionKeyDynamoDB"]["S"]
# Function to repeatedly decrypt until it fails
def deep_decrypt(value):
current = value.encode()
while True:
try:
current = f.decrypt(current)
except Exception:
return current.decode(errors="replace")
final_data = deep_decrypt(data_val)
final_key = deep_decrypt(key_val)
print(f"[Item {idx}]")
print(f" Final Data after deep decrypt: {final_data}")
print(f" Final PartitionKey after deep decrypt: {final_key}")
print()
except Exception as e:
print(f"[Item {idx}] Error: {e}")
```
***
During the CTF, I tried to submit `FLAG{R35p0nd_N0w_D1sc0v3r_F0r3ns1cs}` as the flag but it failed. So I thought that there were another part and wasted alot of time trying the parse the logs to find something different.
It is only until after the CTF ends then I realized I had formatted the flag wrongly 🤦♂️
The flag format is `FLAG-{R35p0nd_N0w_D1sc0v3r_F0r3ns1cs}`
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