{"id":139980,"date":"2025-08-03T11:11:54","date_gmt":"2025-08-03T09:11:56","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/dostizhenie-vypolneniya-koda-pri-kontrole-nad-tekstom-kommentariya-v-python-skripte"},"modified":"2025-08-03T11:11:54","modified_gmt":"2025-08-03T09:11:56","slug":"dostizhenie-vypolneniya-koda-pri-kontrole-nad-tekstom-kommentariya-v-python-skripte","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pl\/blog\/news\/dostizhenie-vypolneniya-koda-pri-kontrole-nad-tekstom-kommentariya-v-python-skripte","title":{"rendered":"Uzyskanie wykonania kodu przy kontroli nad tekstem komentarza w skrypcie Pythona","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Jeden z uczestnik\u00f3w zawod\u00f3w UIUCTF 2025 szczeg\u00f3\u0142owo opisa\u0142, jak uda\u0142o mu si\u0119 wykona\u0107 zadanie, polegaj\u0105ce na uruchomieniu swojego kodu na serwerze, maj\u0105c jedynie mo\u017cliwo\u015b\u0107 zmiany zawarto\u015bci tekstu komentarza w kodzie. <\/p>\n

Uczestnicy mogli wys\u0142a\u0107 zapytanie sieciowe do skryptu Pythona, kt\u00f3ry tworzy\u0142 nowy skrypt Pythona z losow\u0105 nazw\u0105, dodawa\u0142 dane od u\u017cytkownika do tekstu komentarza, usuwaj\u0105c znaki «\n» i «\r», i uruchamia\u0142 ten skrypt poleceniem «python3 nazwa.py». Kontroluj\u0105c jedynie zawarto\u015b\u0107 komentarza, uczestnik musia\u0142 wydoby\u0107 ci\u0105g z pliku «\\\/home\\\/ctfuser\\\/flag». Skrypt by\u0142 tworzony nast\u0119puj\u0105cym kodem: comment = input(«> «).replace(«\n», «»).replace(«\r», «») code = f»»»print(«hello world!») # To jest komentarz. Oto kolejny: # {comment} print(«Thanks for playing!»)»»» <\/p>\n

Zamiast «{comment}» podstawiane by\u0142y dane wprowadzone przez uczestnika, a ostatecznie uruchamiano nast\u0119puj\u0105cy kod: print(«hello world!») # To jest komentarz. Oto kolejny: # Dane, kt\u00f3re wp\u0142yn\u0119\u0142y od uczestnika konkursu print(«Thanks for playing!») <\/p>\n

Zadanie zosta\u0142o stworzone na podstawie podatno\u015bci w parserze CPython, kt\u00f3ry traktowa\u0142 znak z zerowym kodem jako koniec linii (podatno\u015b\u0107 ta mog\u0142a by\u0107 wykorzystana do ukrywania z\u0142o\u015bliwych dzia\u0142a\u0144 w tek\u015bcie komentarza). Problem zosta\u0142 rozwi\u0105zany w wydaniach CPython 3.12.0 i 3.11.4. W u\u017cywanym w konkursie parserze usuwane by\u0142y jedynie znaki «\n» i «\r», ale przy u\u017cyciu podatnej wersji CPython, uczestnik m\u00f3g\u0142 u\u017cy\u0107 znaku «\0» jako separatora. Niemniej jednak ten trik nie zadzia\u0142a\u0142, poniewa\u017c w konkursie u\u017cywana by\u0142a ju\u017c poprawiona wersja CPython, z za\u0142o\u017ceniem, \u017ce w parserze mog\u0105 pozosta\u0107 inne podobne b\u0142\u0119dy, kt\u00f3re uczestnicy b\u0119d\u0105 w stanie zidentyfikowa\u0107. <\/p>\n

Uczestnik, kt\u00f3ry pomy\u015blnie zrealizowa\u0142 zadanie, nie szuka\u0142 nowych podatno\u015bci w parserze, kt\u00f3re pozwoli\u0142yby rozdzieli\u0107 ci\u0105g na cz\u0119\u015bci, lecz skorzysta\u0142 z cechy wykonania w Pythonie plik\u00f3w w zale\u017cno\u015bci od ich zawarto\u015bci. Na przyk\u0142ad, zamiast oryginalnego kodu do pliku z rozszerzeniem «.py» mo\u017cna umie\u015bci\u0107 skompilowany kod bajtowy, przechowywany w plikach z rozszerzeniem «.pyc», i taki plik zostanie wykonany. W omawianym konkursie uczestnik m\u00f3g\u0142 kontrolowa\u0107 jedynie zawarto\u015b\u0107 w \u015brodku pliku, dlatego nie m\u00f3g\u0142 doda\u0107 swojego nag\u0142\u00f3wka w celu zafa\u0142szowania typu MIME. <\/p>\n

Zadanie uda\u0142o si\u0119 rozwi\u0105za\u0107, korzystaj\u0105c z faktu, \u017ce Python od wersji 2.6 mo\u017ce wykonywa\u0107 zawarto\u015b\u0107 archiw\u00f3w ZIP w celu dostarczania pakiet\u00f3w Python w skompresowanej formie. Podobnie jak w przypadku pami\u0119ci podr\u0119cznej bajtkodu, obecno\u015b\u0107 archiwum ZIP okre\u015bla si\u0119 na podstawie zawarto\u015bci, a nie rozszerzenia pliku, tzn. w \u201eplik.py\u201d mo\u017cna umie\u015bci\u0107 archiwum ZIP, a po uruchomieniu polecenia \u201epython plik.py\u201d zostanie ono przetworzone jako skompresowany pakiet Python. Archiwum ZIP w Pythonie jest indeksowane nie wed\u0142ug nag\u0142\u00f3wka na pocz\u0105tku pliku, lecz wed\u0142ug sekcji EOCD (End of Central Directory Record) na ko\u0144cu pliku. W przypadku obecno\u015bci w archiwum pliku \u201e__main__.py\u201d, plik ten jest automatycznie uruchamiany podczas bezpo\u015bredniego uruchamiania archiwum poleceniem \u201epython archiwum.\u201d <\/p>\n

Zadanie konkursowe zosta\u0142o rozwi\u0105zane poprzez wygenerowanie podobnego archiwum ZIP i podstawienie go w tre\u015bci komentarza. Aby zachowa\u0107 poprawno\u015b\u0107 struktury pliku w warunkach obecno\u015bci w ko\u0144cowej cz\u0119\u015bci oryginalnego pliku wywo\u0142ania \u2018print(\u201eThanks for playing!\u201d)\u2019, wykorzystano obecno\u015b\u0107 w sekcji EOCD obszaru komentarza, umieszczonego na samym ko\u0144cu.

\"Uzyskanie<\/center>
\"Uzyskanie<\/center>
\n
\u0179r\u00f3d\u0142o: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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zrealizowa\u0107 zadanie, kt\u00f3re wymaga\u0142o uruchomienia swojego kodu na serwerze, maj\u0105c jedynie mo\u017cliwo\u015b\u0107 zmiany zawarto\u015bci tekstu komentarza.","canonical_url":"https:\/\/prohoster.info\/pl\/blog\/news\/dostizhenie-vypolneniya-koda-pri-kontrole-nad-tekstom-kommentariya-v-python-skripte","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":null,"og:locale":"pl_PL","og:site_name":"ProHoster | \u041a\u0443\u043f\u0438\u0442\u044c \u043d\u0430\u0434\u0435\u0436\u043d\u044b\u0439 \u0445\u043e\u0441\u0442\u0438\u043d\u0433 \u0434\u043b\u044f \u0441\u0430\u0439\u0442\u043e\u0432 \u0441 \u0437\u0430\u0449\u0438\u0442\u043e\u0439 \u043e\u0442 DDoS, VPS VDS \u0441\u0435\u0440\u0432\u0435\u0440\u044b","og:type":"article","og:title":"\ud83e\udd47\u0414\u043e\u0441\u0442\u0438\u0436\u0435\u043d\u0438\u0435 \u0432\u044b\u043f\u043e\u043b\u043d\u0435\u043d\u0438\u044f \u043a\u043e\u0434\u0430 \u043f\u0440\u0438 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