MySQL Authentication Bypass (转载)

[248187] 主题： MySQL Authentication Bypass (转载)

	作者： tshxp. (tshxp.)
	标题： MySQL Authentication Bypass (转载)[转载]
	来自： 202.194..
	发贴时间： 2004年07月07日 22:03:42
	长度： 6689字

	发信人：tshxp@smth.org-SPAM.no (La Traviata)，信区：cn.bbs.comp. security 标题：MySQL Authentication Bypass (转载) 发信站：BBS 水木清华站转信站：FengLin!netnews.sdu.edu.cn!maily.cic.tsinghua.edu.cn!SMT H 【以下文字转载自 BugTraqML 讨论区】发信人: nisr@nextgenss.com (NGSSoftware Insight Security Researc h), 信区: BugTraqML 标题: MySQL Authentication Bypass 发信站: NCTU CSIE FreeBSD Server (Tue Jul 6 05:53:52 2004) 转信站: SMTH!maily.cic.tsinghua.edu.cn!whnet.dhs.org!netnews.sdu .edu.cn!news-ou 出处: freebsd.csie.nctu.edu.tw NGSSoftware Insight Security Research Advisory Name: MySQL Authentication Bypass / Buffer Overflow Systems Affected: MySQL 4.1 prior to 4.1.3, and MySQL 5.0. Severity: High Vendor URL: http://www.mysql.com Author: Chris Anley [ chris@ngssoftware.com ] Date of Advisory: 1st July 2004 Whitepaper ******** We have written a paper that accompanies this advisory. The pape r provides details of various MySQL lockdown techniques, and a rev iew of common attacks on MySQL, including SQL injection. The paper can be found at http://www.ngssoftware.com/papers/HackproofingMySQL.pdf Description ******* "The MySQL database server is the world's most popular open source database." [www.mysql.com]. This advisory details a bug that allows a remote user to entirel y bypass the MySQL password authentication mechanism, allowing them to au thenticate as a MySQL user without knowing that user's password. Using a si milar method, a stack buffer used in the authentication mechanism can be overflowed, though exploitation of the overflow is not straightf orward. Details ***** MySQL 4.1 Authentication Bypass By submitting a carefully crafted authentication packet, it is p ossible for an attacker to bypass password authentication in MySQL 4.1. From check_connection (sql_parse.cpp), line ~837: /* Old clients send null-terminated string as password; new cli ents send the size (1 byte) + string (not null-terminated). Hence in c ase of empty password both send '\0'. / uint passwd_len= thd->client_capabilities & CLIENT_SECU RE_CONNECTION ? passwd++ : strlen(passwd); Provided 0x8000 is specified in the client capabilities flags, t he use can specify the passwd_len field of their choice. For this attack, w e will choose 0x14 (20) which is the expected SHA1 hash length. Several checks are now carried out to ensure that the user is authenticating from a host that is permitted to connect. Provide d these checks are passed, we reach: /* check password: it should be empty or valid / if (passwd_len == acl_user_tmp->salt_len) { if (acl_user_tmp->salt_len == 0 \|\| acl_user_tmp->salt_len == SCRAMBLE_LENGTH & & check_scramble(passwd, thd->scramble, acl_user_ tmp->salt) == 0 \|\| check_scramble_323(passwd, thd->scramble, (ulong ) acl_user_tmp->salt ) == 0) { acl_user= acl_user_tmp; res= 0; } } the check_scramble function fails, but within the check_scramble _323 function we see: my_bool check_scramble_323(const char scrambled, const char message, ulong hash_pass) { struct rand_struct rand_st; ulong hash_message[2]; char buff[16],to,extra; /* Big enough fo r check / const char pos; hash_password(hash_message, message, SCRAMBLE_LENGTH_323); randominit(&rand_st,hash_pass[0] ^ hash_message[0], hash_pass[1] ^ hash_message[1]); to=buff; for (pos=scrambled ; pos ; pos++) to++=(char) (floor(my_rnd(&rand_st)31)+64); extra=(char) (floor(my_rnd(&rand_st)31)); to=buff; while (scrambled) { if (scrambled++ != (char) (to++ ^ extra)) return 1; / Wrong passwor d / } return 0; } At this point, the user has specified a 'scrambled' string that is as long as they wish. In the case of the straightforward authentication bypass, this is a zero-length string. The final loop compares each chara cter in the 'scrambled' string against the string that mysql knows is th e correct response, until there are no more characters in 'scrambled'. Sin ce there are no characters at all* in 'scrambled', the function returns '0' immediately, allowing the user to authenticate with a zero-lengt h string. This bug is relatively easy to exploit, although it is necessary to write a custom MySQL client in order to do so. In addition to the zero-length string authentication bypass, the stack-based buffer 'buff' can be overflowed by a long 'scramble' string. The buffer is overflowed with characters output from my_rnd(), a pseudo random number generator. The characters are in the range 0x40..0 x5f. On some platforms, arbitrary code execution is possible, though the exploit is complex and requires either brute force, or knowledge of at l east one password hash. Fix Information and workarounds ***************************** MySQL AB were contacted on the 1st of June 2004 and the patch fo r this bug was present in the source code by the 2nd of June. Since MySQL p refer users to install via pre-built binary packages, NGS have delayed the release of this advisory until appropriate 'patch' packages were available. MySQL AB have fixed this bug in version 4.1.3, and the most rece nt builds of version 5.0. In addition to patching, various workarounds are possible for th is bug. The attacker must know or be able to guess the name of a user in order for this attack to work, so renaming the default MySQL 'root' ac count is a reasonable precaution. Also, the account in question must be a ccessible from the attacker's host, so applying ip-address based login res trictions will also mitigate this bug. A check for this vulnerability has been added to Typhon III, NGS Software's advanced vulnerability assessment scanner. For more information please visit the NGSSoftware website at http://www.ngssoftware.com/ About NGSSoftware *************** NGSSoftware design, research and develop intelligent, advanced a pplication security assessment scanners. Based in the United Kingdom, NGSSo ftware have offices in the South of London and the East Coast of Scotla nd. NGSSoftware's sister company NGSConsulting, offers best of breed security consulting services, specializing in application, host and netwo rk security assessments. http://www.ngssoftware.com/ Telephone +44 208 401 0070 Fax +44 208 401 0076 enquiries@ngssoftware.com
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