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SHITTR SERVICE

KNOWN ISSUES / WON'T FIX

  • CSRF is possible, but not of much use?
  • No follow restriction limit in GET.sh (g_follow_shittr), because followCnt does not exist (should be follow_cnt) => red herring - nothing is done with that restriction anyway

CONFIRMED VULNS

2nd line of file read - Exploit: n (but works)

  • In db.sh, get_user the raw cookie value is passed to cat + sed, which will return the 2nd line from a file as the user name
  • I cannot think of an exploit :-/
  • FIX: Dunno? Properly chroot/escape the file name

Auth bypass 1 - Exploit: y

  • In dh.sh, the service generates seemingly strong (dd if=/dev/urandom) session IDs, but those are only 3-4 characters long, thus brute-forceable.
  • An attacker could BF a valid session within the deletion timeout of 15 min, because /logout does not delete the sessions. With valid sessions, the attacker could look for flags.
  • FIX: Use longer session ids

Visibility Bypass 1 - Exploit: n (but works!)

  • Viewing a 'private' user's profile and shits is possible at /@
  • The attacker cannot see private user's shits on /diarrhea or /shittrs
  • The attacker can, however, see those accounts mentioned in shits OR through an account B that the hidden user is following (B's following shittr list)
  • FIX: Prohibit access to hidden user's profiles
  • CHECKER ---> Register ---> Set private ---> Post shit with flag ---> Post public shit with "@" just took a dump.

Visibility Bypass 2 - Exploit: no (but works!)

  • Viewing a hidden user's shits is possible at /tag/
  • The attacker could guess the hashtags #flag or #enowars and monitor those for shits from the gamebot with a flag
  • FIX: Filter hidden user's shits from the hashtag
  • CHECKER ---> Register ---> Set private ---> Post shit with flag ---> Post public shit with "#enowars" hashtag

Visibility Bypass 3 - Exploit: no (but works!)

  • If one unfollows himself, then the matching ids-Array in db.sh (fluid_diarrhea) is (), which matches all entries and therefore all shits are displayed.

Info leak 1 / Crypto 2 - Exploit: no (but works!)

  • Directory listing is enabled for /static/, or folders in general
  • People can leak the ssl private key and/or the encryption key
  • FIX: Disable Directory Listing and/or block access to the files

Info leak 2 - Exploit: no (but works!)

  • HEAD requests can be used to check if folders or files exist
  • FIX: Do not allow path traversal

Info leak 3 - Exploit: no (but works!)

  • The HEAD.sh contains a regex that matches against $DEBUG and will happily give away the last 500 lines of debug log. (even if DEBUG=0, bc an URL with a '0' or '1' will match)
  • The attacker can obtain flags
  • Debug log contains the session id (rand number)
  • FIX: Remove the debug log retrieval in HEAD.sh

Info leak 4'- Exploit: no (but works!)

  • If the user is an admin, GET /log will display the last 100 entries for the requesting IP address
  • FIX: None (only allow admins to become admins!)

ADMIN BYPASS 1 - Exploit: no (but works!)

  • Register a user name that matches /admin/
  • The is_admin middleware checks $DEBUG for it's string length (-n), so it will always be true for DEBUG=0 and DEBUG=1
  • The attacker can therefore gain "ADMIN=1" easily
  • With that, the attacker can view /diarrhea and /shittrs or hidden user's without restrictions
  • FIX: Remove "-n" in the is_admin middleware

ADMIN BYPASS 2 - Exploit: y (but works!)

  • Use the "image-in-tweet" functionality to write a user file to ./users/.user with Admin=1
  • This can be achieved by an attacker by abusing the create_shit() function in db.sh. The regex will match arbitrary paths that contain ".png", e.g. /.png/foo.user would work. The cut -d'/' check can be bypassed, because the final file path is urldecoded again (thus using ..%2f) works.
  • FIX: Remove the urldecode on the file path and/or fix the regex to only allow .png files
  • TODO: Maybe

Crypto 1 - Exploit: yes (but works!)

  • The server.sh includes /bin/ in the PATH, so that the our "shit/openssl" tool is called instead of openssl in utils.sh
  • Uses simple ECB with the first 16 bytes as the key from enc.key to encrypt shits.
  • Shits can be downloaded from /settings, so one can obtain plaintext + ciphertext pairs to recover the key.
  • The key can then be used to decrypt other people's private shits!
  • FIX: Use more than 16 bytes and/or other crypto algorithm

RCE 2 - Exploit ??? (only when unpatched file write)

  • The shitssl binary has 2 BOFs, of which one is exploitable by creating a file e.g. in the shitposts directory, which will be read and tried to decrypt by the binary.
  • If the base64 decoded strings is > 2048 bytes, then it will copy more than it's allowed into a buffer and result in an easy BOF
  • FIX: Patch binary and/or limit lengths

RCE 1 (?) - Exploit ??? (only when unpatched file write)

  • The p_downloadshit function creates a tar archive with unquoted expansion *
  • This might (?!) result in a vulnerability like RCE
  • FIX: Make tar secure

Ideas

  • I'll probably add some subtle RCE

  • Maybe some SQL or Template injection or so (?)

  • Maybe some debug options that leak flags?

  • Bild-Fetcher nochmal debuggen, ob nicht file://etc/passwd#test.png oder so geht. Redirect von HTTP ist in libcurl deaktiviert

  • Implement language choosing based on the Accept-Header

  • Implement answering to shits

  • (?) Statuscode ist Stunden seit EPOCH Module $realStatuscode

Bugs

  • When removing shits, also remove them from the diarrhea.log

  • If PATH=$PATH:/bin/ is removed, then the real openssl is used -> No RCE2, Crypto1

  • Make the shit-ID not so random (e.g. online the time it was posted, or smth that can be known/brute-forced)

  • Add @gehaxelt in the footer + server time + rendering time

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A twitter clone and webframework + webserver in pure bash as a challenge for ENOWARS3

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