-----BEGIN PGP SIGNED MESSAGE----- MIT krb5 Security Advisory 2003-003 2003-03-18 Topic: faulty length checks in xdrmem_getbytes Severity: serious SUMMARY ======= The MIT Kerberos 5 implementation includes an RPC library derived from SUNRPC. We have been notified that the xdrmem_getbytes() function contains faulty length checks. These length checks are vulnerable to an integer overflow, which may be exploitable to create denials of service or to gain unauthorized access to sensitive information. An attacker who has successfully authenticated to the Kerberos administration daemon (kadmind) may be able to crash kadmind or induce it to leak sensitive information, such as secret keys. For the attack to succeed, it is believed that the configuration of the kadmind installation must allow it to successfully allocate more than INT_MAX bytes of memory. IMPACT ====== * An attacker capable of authenticating to kadmind may be able to crash kadmind. * Under extremely unlikely circumstances, an attacker capable of authenticating to kadmind may be able to induce it to return sensitive information, such as secret keys. AFFECTED SOFTWARE ================= * All releases of MIT Kerberos 5, up to and including krb5-1.2.7. FIX === Apply the following patch to src/lib/rpc/xdr_mem.c and rebuild your tree. Index: xdr_mem.c =================================================================== RCS file: /cvs/krbdev/krb5/src/lib/rpc/xdr_mem.c,v retrieving revision 1.8 diff -c -r1.8 xdr_mem.c *** xdr_mem.c 1998/02/14 02:27:24 1.8 - --- xdr_mem.c 2003/02/04 22:57:24 *************** *** 47,52 **** - --- 47,54 ---- #include #include #include + #include + #include static bool_t xdrmem_getlong(); static bool_t xdrmem_putlong(); *************** *** 83,89 **** xdrs->x_op = op; xdrs->x_ops = &xdrmem_ops; xdrs->x_private = xdrs->x_base = addr; ! xdrs->x_handy = size; } static void - --- 85,91 ---- xdrs->x_op = op; xdrs->x_ops = &xdrmem_ops; xdrs->x_private = xdrs->x_base = addr; ! xdrs->x_handy = (size > INT_MAX) ? INT_MAX : size; /* XXX */ } static void *************** *** 98,105 **** long *lp; { ! if ((xdrs->x_handy -= sizeof(rpc_int32)) < 0) return (FALSE); *lp = (long)ntohl(*((rpc_u_int32 *)(xdrs->x_private))); xdrs->x_private += sizeof(rpc_int32); return (TRUE); - --- 100,109 ---- long *lp; { ! if (xdrs->x_handy < sizeof(rpc_int32)) return (FALSE); + else + xdrs->x_handy -= sizeof(rpc_int32); *lp = (long)ntohl(*((rpc_u_int32 *)(xdrs->x_private))); xdrs->x_private += sizeof(rpc_int32); return (TRUE); *************** *** 111,118 **** long *lp; { ! if ((xdrs->x_handy -= sizeof(rpc_int32)) < 0) return (FALSE); *(rpc_int32 *)xdrs->x_private = (rpc_int32)htonl((rpc_u_int32)(*lp)); xdrs->x_private += sizeof(rpc_int32); return (TRUE); - --- 115,124 ---- long *lp; { ! if (xdrs->x_handy < sizeof(rpc_int32)) return (FALSE); + else + xdrs->x_handy -= sizeof(rpc_int32); *(rpc_int32 *)xdrs->x_private = (rpc_int32)htonl((rpc_u_int32)(*lp)); xdrs->x_private += sizeof(rpc_int32); return (TRUE); *************** *** 125,132 **** register unsigned int len; { ! if ((xdrs->x_handy -= len) < 0) return (FALSE); memmove(addr, xdrs->x_private, len); xdrs->x_private += len; return (TRUE); - --- 131,140 ---- register unsigned int len; { ! if (xdrs->x_handy < len) return (FALSE); + else + xdrs->x_handy -= len; memmove(addr, xdrs->x_private, len); xdrs->x_private += len; return (TRUE); *************** *** 139,146 **** register unsigned int len; { ! if ((xdrs->x_handy -= len) < 0) return (FALSE); memmove(xdrs->x_private, addr, len); xdrs->x_private += len; return (TRUE); - --- 147,156 ---- register unsigned int len; { ! if (xdrs->x_handy < len) return (FALSE); + else + xdrs->x_handy -= len; memmove(xdrs->x_private, addr, len); xdrs->x_private += len; return (TRUE); *************** *** 179,185 **** { rpc_int32 *buf = 0; ! if (xdrs->x_handy >= len) { xdrs->x_handy -= len; buf = (rpc_int32 *) xdrs->x_private; xdrs->x_private += len; - --- 189,195 ---- { rpc_int32 *buf = 0; ! if (len >= 0 && xdrs->x_handy >= len) { xdrs->x_handy -= len; buf = (rpc_int32 *) xdrs->x_private; xdrs->x_private += len; The patch was generated against krb5-1.2.7; patches to other releases may apply with some offset. This patch may also be found at: http://web.mit.edu/kerberos/www/advisories/2003-003-xdr_patch.txt The associated detached PGP signature is at: http://web.mit.edu/kerberos/www/advisories/2003-003-xdr_patch.txt.asc REFERENCES ========== This announcement and related security advisories may be found on the MIT Kerberos security advisory page at: http://web.mit.edu/kerberos/www/advisories/index.html The main MIT Kerberos web page is at: http://web.mit.edu/kerberos/www/index.html CERT VU#516825 http://www.kb.cert.org/vuls/id/516825 CVE CAN-2003-0028 http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0028 ACKNOWLEDGMENTS =============== Thanks to CERT for notifying us of this vulnerability. DETAILS ======= The xdrmem_getbytes() function decrements the private signed integer "xdrs->x_handy" by the supplied length "len", which is an unsigned int. It then verifies that the resulting value of "xdrs->x_handy" is non-negative. Using a carefully chosen value of "len" (so that it is greater than INT_MAX), it is possible for this check to succeed even if the value of "len" would cause the buffer to be overrun on read. This overrun may result in a segmentation fault, or in the unauthorized copying of sensitive information. A mitigating factor is that most call chains that end up calling xdrmem_getbytes() first call malloc() (via the mem_alloc() macro) to allocate a buffer of the requested length. This allocation of more than INT_MAX bytes will fail on most configurations due to internal limitations of malloc() or due to system resource limits. On systems where allocation of more than INT_MAX bytes can succeed (possibly including 64-bit environments), the probability of successful exploit is higher. In MIT krb5, the vulnerable invocations of xdrmem_getbytes() inside kadmind only occur after the user has successfully authenticated. Additionally, any unauthorized copies of sensitive data obtained by exercising this vulnerability are extremely unlikely to be returned to the remote client. REVISION HISTORY ================ 2003-03-18 original release -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.7 (SunOS) iQCVAwUBPnd5J6bDgE/zdoE9AQEIeAQAxuMhSNtC94YhIqQcuhRsKXFf/T8T8lh6 YUeTNaqA9sQkZBE2sZEyI4uq0iiZjwQyUfhylcPbEaIX3f9dto8YWmRvPztsvIQR jzAlRU4o7//kw2oWu1JQC0FNpcifr1D1j0E59xqjDaCGDa6LlMFqd/V77pHKIcLU c0DO4+ORljY= =54iC -----END PGP SIGNATURE-----