MITKRB5-SA-2008-002: array overrun in RPC library used by kadmin

2008-03-19T00:00:00
ID SECURITYVULNS:DOC:19442
Type securityvulns
Reporter Securityvulns
Modified 2008-03-19T00:00:00

Description

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MITKRB5-SA-2008-002

MIT krb5 Security Advisory 2008-002 Original release: 2008-03-18 Last update: 2008-03-18

Topic: array overrun in RPC library used by kadmind

CVE-2008-0947, CVE-2008-0948 VU#374121 Use of high-numbered file descriptors in the RPC library, used by kadmind, can cause references past the end of an array.

CVSSv2 Vector: AV:N/AC:L/Au:N/C:C/I:C/A:C/E:P/RL:T/RC:C

CVSSv2 Base Score: 10

Access Vector: Network Access Complexity: Low Authentication: None Confidentiality Impact: Complete Integrity Impact: Complete Availability Impact: Complete

CVSSv2 Temporal Score: 7.8

Exploitability: Proof-of-Concept Remediation Level: Official fix Report Confidence: Confirmed

SUMMARY

Two bugs in the RPC library server code, used in the kadmin server, causes an array overrun if too many file descriptors are opened. Memory corruption can result.

IMPACT

An unauthenticated remote attacker can cause memory corruption in the kadmind process, which is likely to cause kadmind to crash, resulting in a denial of service. It is at least theoretically possible for such corruption to result in database corruption or arbitrary code execution, though we have no such exploit and are not aware of any such exploits in use in the wild.

CVE-2008-0947: In 1.4 and later, this bug can only be triggered in configurations that allow large numbers of open file descriptors in a process.

CVE-2008-0948: In versions before 1.3, this bug can be triggered in similar circumstances, but is further limited to platforms not defining certain macros in certain C system header files. Solaris 10 and Mac OS X 10.4 appear to be unaffected, while GNU libc systems (e.g., many GNU/Linux distributions) are. It appears that in at least some cases kadmind will simply exit after getting a "bad file descriptor" error, but this cannot be guaranteed.

AFFECTED SOFTWARE

CVE-2008-0947: libgssrpc and kadmind, from krb5-1.4 through krb5-1.6.3

CVE-2008-0948: libgssrpc and kadmind, in krb5-1.2.2 and probably most other versions before 1.3, on systems where <unistd.h> does not define FD_SETSIZE.

FIXES

  • Workaround: Check the system header files for the value of FD_SETSIZE. Use "ulimit -n" or "limit descriptors" in the shell invoking kadmind to limit the number of open file descriptors to FD_SETSIZE or less, before starting kadmind. Then the operating system will prevent the use of file descriptors large enough to exploit this bug.

  • Apply the following patch for krb5-1.4 and later:

=== src/lib/rpc/svc.c

  • --- src/lib/rpc/svc.c (revision 1666) +++ src/lib/rpc/svc.c (local) @@ -109,15 +109,17 @@ if (sock < FD_SETSIZE) { xports[sock] = xprt; FD_SET(sock, &svc_fdset);
  • if (sock > svc_maxfd)
  • svc_maxfd = sock; } #else if (sock < NOFILE) { xports[sock] = xprt; svc_fds |= (1 << sock);
  • if (sock > svc_maxfd)
  • svc_maxfd = sock; } #endif / def FD_SETSIZE /
    • if (sock > svc_maxfd)
    • svc_maxfd = sock; }

/ === src/lib/rpc/svc_tcp.c ================================================================== - --- src/lib/rpc/svc_tcp.c (revision 1666) +++ src/lib/rpc/svc_tcp.c (local) @@ -54,6 +54,14 @@ extern errno; /

+#ifndef FD_SETSIZE +#ifdef NBBY +#define NOFILE (sizeof(int) * NBBY) +#else +#define NOFILE (sizeof(int) * 8) +#endif +#endif + / * Ops vector for TCP/IP based rpc service handle / @@ -215,6 +223,19 @@ register SVCXPRT xprt; register struct tcp_conn cd;

+#ifdef FD_SETSIZE + if (fd >= FD_SETSIZE) { + (void) fprintf(stderr, "svc_tcp: makefd_xprt: fd too high\n"); + xprt = NULL; + goto done; + } +#else + if (fd >= NOFILE) { + (void) fprintf(stderr, "svc_tcp: makefd_xprt: fd too high\n"); + xprt = NULL; + goto done; + } +#endif xprt = (SVCXPRT )mem_alloc(sizeof(SVCXPRT)); if (xprt == (SVCXPRT )NULL) { (void) fprintf(stderr, "svc_tcp: makefd_xprt: out of memory\n"); @@ -271,6 +292,10 @@ * make a new transporter (re-uses xprt) */ xprt = makefd_xprt(sock, r->sendsize, r->recvsize); + if (xprt == NULL) { + close(sock); + return (FALSE); + } xprt->xp_raddr = addr; xprt->xp_addrlen = len; xprt->xp_laddr = laddr;

This patch will result in too-high-numbered file descriptors being immediately closed after the connection comes in. Clients will see connections established, and then closed; a "GSS-API (or Kerberos) error while initializing kadmin interface" will eventually result. Once some of the lower-numbered file descriptors are closed, clients will be able to get useful connections again.

  • Apply the following patch for krb5-1.2.2 and probably other pre-1.3 versions:

Index: src/lib/rpc/rpc_dtablesize.c

  • --- src/lib/rpc/rpc_dtablesize.c (revision 20237) +++ src/lib/rpc/rpc_dtablesize.c (working copy) @@ -32,6 +32,7 @@ #endif

#include <unistd.h> +#include <gssrpc/rpc.h>

/* * Cache the result of getdtablesize(), so we don't have to do an

  • The next release from MIT (1.6.4) will include a fix.

REFERENCES

This announcement is posted at:

http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2008-002.txt

This announcement and related security advisories may be found on the MIT Kerberos security advisory page at:

    http://web.mit.edu/kerberos/advisories/index.html

The main MIT Kerberos web page is at:

    http://web.mit.edu/kerberos/index.html

CVSSv2:

http://www.first.org/cvss/cvss-guide.html
http://nvd.nist.gov/cvss.cfm?calculator&amp;adv&amp;version=2

CVE: CVE-2008-0947 http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-0947

CVE: CVE-2008-0948 http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-0948

CERT: VU#374121 http://www.kb.cert.org/vuls/id/374121

ACKNOWLEDGMENTS

Thanks to Jeff Altman of Secure Endpoints for discovering and reporting this problem in 1.6.3.

Thanks to the Red Hat Security Response Team for noting that 1.2.2 was also affected by the same problem, for different reasons.

CONTACT

The MIT Kerberos Team security contact address is <krbcore-security@mit.edu>. When sending sensitive information, please PGP-encrypt it using the following key:

pub 1024D/2915318C 2008-01-18 [expires: 2009-02-01] uid MIT Kerberos Team Security Contact <krbcore-security@mit.edu> sub 2048g/3A91A276 2008-01-18 [expires: 2009-02-01]

DETAILS

The variable svc_maxfd tracks the highest-numbered file descriptor registered with the RPC library as a transport handle. While the registration function does check that the file descriptor number is less than FD_SETSIZE for array references, the code for updating svc_maxfd is not so protected. Elsewhere, svc_maxfd is used as an upper bound for array indexing, and as the maximum file descriptor number to pass to select().

In 1.2.2, the variable is called max_xport, and is checked against the value returned by _gssrpc_rpc_dtablesize(), but while that function checks FD_SETSIZE if it's defined, the source file containing it only includes unistd.h, which doesn't define FD_SETSIZE on all platforms. In kadmind, the value from _gssrpc_rpc_dtablesize() is also passed to select() as the maximum file descriptor number.

REVISION HISTORY

2008-03-18 original release

Copyright (C) 2008 Massachusetts Institute of Technology -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (Darwin)

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