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Linux 2.x smbfs Multiple Remote Vulnerabilities
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SUMMARY
Linux is a clone of the operating system Unix, written from scratch by
Linus Torvalds with assistance from a loosely-knit team of hackers across
the Net. It aims towards POSIX and Single UNIX Specification compliance.
During an audit of the smb filesystem implementation within Linux several
vulnerabilities were discovered ranging from out of bounds read accesses
to kernel level buffer overflows.
To exploit any of these vulnerabilities an attacker needs control over the
answers of the connected smb server. This could be achieved by man in the
middle attacks or by taking over the smb server with the recently
disclosed vulnerability in Samba 3.x
While any of these vulnerabilities can be easily used as remote denial of
service exploits against Linux systems, it is unclear if it is possible
for a skilled local or remote attacker to use any of the possible buffer
overflows for arbitrary code execution in kernel space.
DETAILS
Vulnerable Systems:
* Linux version 2.4.27 and prior
* Linux version Linux 2.7 up to 2.6.9
Immune Systems:
* Linux version 2.4.28 and newer
01 - smb_proc_read(X) malicious data count overflow:
Affected Kernels: 2.4
When receiving the answer to a read(X) request the Linux 2.4 kernel trusts
the returned data count and copies exactly that amount of bytes into the
output buffer. This means any call to the read syscall on a smb filesystem
could result in an overflow withing kernel memory if the connected smb
server returns more data than requested. While this is a trivial to
exploit DOS vulnerability it is unclear if it can be used by a skilled
attacker to execute arbitrary code.
02 - smb_proc_readX malicious data offset information leak:
Affected Kernels: 2.4
When receiving the answer to a readX request the Linux 2.4 kernel does not
properly bounds check the supplied data offset. The check in place can
fail because of a signedness issue. This means that a local attacker can
leak kernel memory simply by issuing the read syscall on a smb filesystem
when the connected server returns a data offset from outside the packet.
This can of course also lead to a kernel crash when unallocated memory is
accessed.
03 - smb_receive_trans2 defragmentation overflow:
Affected Kernels: 2.4
At the end of the TRANS2 defragmentation process the complete packet is
moved to another place if a certain condition is true. In combination with
[07] and the fact that the counters are not bounds checked before copying
the data this can result in a kernel memory overflow.
04 - smb_proc_readX_data malicious data offset DOS:
Affected Kernels: 2.6
The server supplied data offset is decremented by the header size and then
used as offset within the packet. While the supplied offset is checked
against an upper bound it may have underflowed and therefore point outside
the allocated memory. Any access to that memory could result in a crash.
05 - smb_receive_trans2 malicious parm/data offset info leak/DOS:
Affected Kernels: 2.4, 2.6
Both versions of the kernel do not properly bounds check the server
supplied packet based offset of the parameters/data sent. This results in
smbfs copying data from memory outside the received smb fragment into the
receiving buffer. This can leak kernel memory to the calling function or
result in a DOS because of accesses to unallocated memory.
06 - smb_recv_trans2 missing fragment information leak:
Affected Kernels: 2.4, 2.6
The defragmentation process of TRANS2 SMB packets does not properly
initialize the receiving buffer. An attacker may f.e. send several
thousand times the first byte of a packet until the received data count
reaches the expected total and so leaks the rest of the uninitialized
receiving buffer to the calling function.
07 - smb_recv_trans2 fragment resending leads to invalid counters:
Affected Kernels: 2.4, 2.6
The defragmentation termination condition is that at least the expected
parameter count and at least the expected data count is reached. By using
the fragment resending technique an attacker can increase one of those
counters to an arbitrary high value.
Disclosure Timeline:
25. Sep 2004 Made initial contact with the Linux Developers
27. Sep 2004 Contacted vendor-sec about this issue
22. Oct 2004 Sent the 2nd round of smbfs vulnerabilities to both parties
27. Oct 2004 Sent final patchset for 2.4 and 2.6 kernel to the developers
11. Nov 2004 Linux 2.4.28-rc3 containing the final patchset was made
available by the developers
17. Nov 2004 Linux 2.4.28 released
17. Nov 2004 Public Disclosure
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0883>
CAN-2004-0883
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0949>
CAN-2004-0949
ADDITIONAL INFORMATION
The information has been provided by <mailto:s.esser@ematters.de> Stefan
Esser.
The original article can be found at:
<http://security.e-matters.de/advisories/142004.html?SID=9452714072161c5f25d7312c0d23c30b>
http://security.e-matters.de/advisories/142004.html?SID=9452714072161c5f25d7312c0d23c30b
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