Re: [Full-disclosure] Fwd: VSFTPD Remote Heap Overrun (low severity)

[Daniel J Walsh <dwalsh@xxxxxxxxxx>]

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On 12/12/2011 11:22 AM, Ramon de C Valle wrote:
>> I havent looked into it yet, just saw the 0x41414141 in the
>> registers and assumed it is exploitable.I will have a look into
>> it when I find time and post the results here.
> Just some additional information about what probably happened in
> your case, and why I've asked if this behaviour is consistent.
> 
> In Red Hat Enterprise Linux 6, vsftpd-2.2.2, and glibc 2.12:
> 
> [...]
> 
> (gdb) c Continuing.
> 
> Program received signal SIGABRT, Aborted. 0x009c2424 in
> __kernel_vsyscall () (gdb) bt #0  0x009c2424 in __kernel_vsyscall
> () #1  0x001bdd31 in raise () from /lib/libc.so.6 #2  0x001bf60a in
> abort () from /lib/libc.so.6 #3  0x001fbd5d in __libc_message ()
> from /lib/libc.so.6 #4  0x002021a1 in malloc_printerr () from
> /lib/libc.so.6 #5  0x00222ca3 in __tzfile_read () from
> /lib/libc.so.6 #6  0x00222348 in tzset_internal () from
> /lib/libc.so.6 #7  0x00222491 in __tz_convert () from
> /lib/libc.so.6 #8  0x0022078f in localtime () from /lib/libc.so.6 
> #9  0x00180f1d in ?? () #10 0x001769de in ?? () #11 0x00176cb8 in
> ?? () #12 0x001701aa in ?? () #13 0x00172758 in ?? () #14
> 0x0017a46e in ?? () #15 0x0017a937 in ?? () #16 0x0016d58d in main
> () (gdb) f 5 #5  0x00222ca3 in __tzfile_read () from
> /lib/libc.so.6 (gdb) i r eax            0x0   0 ecx            0x53e
> 1342 edx            0x6       6 ebx            0x319ff4       3252212 esp
> 0xbfb34fc8    0xbfb34fc8 ebp            0xbfb350dc    0xbfb350dc esi
> 0x1f4 500 edi            0x12cf0f8    19722488 eip            0x222ca3
> 0x222ca3 <__tzfile_read+83> eflags         0x200202   [ IF ID ] cs
> 0x73  115 ss             0x7b 123 ds             0x7b 123 es
> 0x7b  123 fs             0x0  0 gs             0x33   51 (gdb) x/i
> $eip => 0x222ca3 <__tzfile_read+83>:  movl   $0x0,0x9c0(%ebx) (gdb)
> i r ebx ebx            0x319ff4       3252212 (gdb) x/x $ebx+0x9c0 
> 0x31a9b4 <transitions>:       0x012ce928 (gdb) x/i $eip => 0x222ca3
> <__tzfile_read+83>:   movl   $0x0,0x9c0(%ebx) (gdb) 0x222cad
> <__tzfile_read+93>:   lea    -0xc(%ebp),%esp (gdb) 0x222cb0
> <__tzfile_read+96>:   pop    %ebx (gdb) 0x222cb1 <__tzfile_read+97>:
> pop    %esi (gdb) 0x222cb2 <__tzfile_read+98>:        pop    %edi (gdb) 
> 0x222cb3 <__tzfile_read+99>:  pop    %ebp (gdb) 0x222cb4
> <__tzfile_read+100>:  ret (gdb)
> 
> As I mentioned, this is detected by glibc when freeing our
> controlled chunk (i.e. transitions), before returning from
> __tzfile_read. In the video, I see you used dividead's exploit
> without change, thus malloc(0) most likely allocated from fast
> bins, and you probably had the __tzfile_read (i.e. f) file
> structure allocated nearby within the ~50000 adjacent bytes, and
> had this corrupted at some place in main arena (since file
> structures are larger than 64 bytes and will not be allocated from
> fast bins). You probably will see this behaviour repeat, but most
> likely the file structure will not be located at the same offset in
> your buffer.
> 
> For SELinux, unfortunately it seems that with the appropriate
> configuration of "allow_ftpd_full_access" disabled and
> "ftp_home_dir" enabled, a vsftpd process chrooted and confined
> (i.e. ftpd_t) allow locale files to be opened not having the
> locale_t type (i.e. user_home_t, in this case), which if don't
> allow would have completely mitigated this issue. Dan, could you
> fix this in SELinux policy?
> 
> Thanks,
> 
Ramon, not sure I understand, what are you trying to prevent here?
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