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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2015.2094 Cisco ASA Unicast Reverse Path Forwarding (uRPF) Bypass Vulnerability 13 August 2015 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Cisco ASA Publisher: Cisco Systems Operating System: Cisco Impact/Access: Reduced Security -- Remote/Unauthenticated Resolution: Mitigation CVE Names: CVE-2015-4321 Original Bulletin: http://tools.cisco.com/security/center/viewAlert.x?alertId=40440 - --------------------------BEGIN INCLUDED TEXT-------------------- Vulnerability Alert Cisco ASA Unicast Reverse Path Forwarding (uRPF) Bypass Vulnerability Threat Type: CWE-20: Input Validation IntelliShield ID: 40440 Version: 1 First Published: 2015 August 12 18:05 GMT Last Published: 2015 August 12 18:05 GMT Port: Not available CVE: CVE-2015-4321 Urgency: Unlikely Use Credibility: Confirmed Severity: Mild Damage CVSS Base: 5.0 CVSS Temporal: 4.8 Version Summary: Cisco Adaptive Security Appliance contains a vulnerability that could allow an unauthenticated, remote attacker to bypass security restrictions. Updates are not available. Description A vulnerability in the Unicast Reverse Path Forwarding (uRPF) feature in the Cisco Adaptive Security Appliance (ASA) could allow an unauthenticated, remote attacker to bypass the uRPF validation checks. The vulnerability is due to incorrect uRPF validation where IP packets from an outside interface, whose IP address is both in the ASA routing table and associated with an internal interface, are not dropped. An attacker could exploit this vulnerability by sending spoofed IP packets to the ASA in a subnet range that should be dropped. An exploit could allow the attacker to bypass uRPF validation on the ASA and the packet will be incorrectly forwarded on the internal network. Cisco has confirmed the vulnerability; however, software updates are not available. Warning Indicators At the time this alert was first published, Cisco ASA Software Releases 9.3(1.50), 9.3(2.100), 9.3(3), and 9.4(1) were vulnerable. Later releases of Cisco ASA Software may also be vulnerable. IntelliShield Analysis To exploit this vulnerability, the targeted device must have the ip verfiy reverse-path interface command set on an outside interface and the interface must have a default route configured. In addition, the attacker must know a subnet range set on the targeted device that is configured to drop packets prior to sending spoofed IP packets to the device. Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available. Vendor Announcements Cisco has released bug ID CSCuv60724 for registered users, which contains additional details and an up-to-date list of affected product versions. Impact An unauthenticated, remote attacker could exploit this vulnerability to bypass uRPF validation checks on an affected device. An exploit could allow the attacker to incorrectly forward packets on the internal network. Technical Information The vulnerability is due to incorrect uRPF validation where IP packets from an outside interface, whose IP address is both in the ASA routing table and associated with an internal interface, are not dropped. An unauthenticated, remote attacker could exploit this vulnerability by sending spoofed IP packets to a targeted ASA in a subnet range that should be dropped. An exploit could allow the attacker to bypass uRPF validation on the ASA which would cause packets to be incorrectly forwarded on the internal network. Safeguards Administrators are advised to contact the vendor regarding future updates and releases. Administrators can help protect affected systems from external attacks by using a solid firewall strategy. Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems. Administrators are advised to monitor affected systems. Patches/Software Software updates are not available. Alert History Initial Release Product Sets The security vulnerability applies to the following combinations of products. Primary Products: Cisco Cisco Adaptive Security Appliance (ASA) Software 9.3 .3, (2.100), (1.50) | 9.4 .1 Associated Products: N/A LEGAL DISCLAIMER The urgency and severity ratings of this alert are not tailored to individual users; users may value alerts differently based upon their network configurations and circumstances. THE ALERT, AND INFORMATION CONTAINED THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE ALERT, AND INFORMATION CONTAINED THEREIN, OR MATERIALS LINKED FROM THE ALERT, IS AT YOUR OWN RISK. INFORMATION IN THIS ALERT AND ANY RELATED COMMUNICATIONS IS BASED ON OUR KNOWLEDGE AT THE TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT NOTICE. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME. - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. 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On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBVcwAZn6ZAP0PgtI9AQLxUhAArLn5S90cTvp8Bxgh5X6nFJyP8JVXFDUl yXWXudFloEEnBNFUFSUEjSCEHcSFLUqADrZliY+eIpg7VicavXyxKGIRZr4ycqDT OcBLqI2gBBYAsZYaTAHKeQdxisp06vi53XSajqr6RcHTmBKX/j3Dtg2ZUxPVUWPX PdG0Dt4GxCZ0gbeM4qAEWNFGegEj8TeYU7V3ZuaqQyhMVvzXH3pgFQUFrPCcoJ1b tXObpxPB5je3RQIFYib1aIVZ1kEr2L6FjPeww/+rMz4bG5qa0Za5RS7DOIXHyDtk IIFAFmBHIFlEJ4Ru6LNotYCE2mvZ/2l3nzSo96h8ijwZuXBBRFeEbqxL2WYTI0IR IHQDpDdHMni6/YUv8pa1jFlWgQYFtnoMJSfMHsE5lHOLZf581VBeHpCW+4skPHPq KJusX/D1R8+wa1sMTFkUiUIXl2I3pJ/ITW0XDP9mqvCv7UGzlBXJTuKafEv5+5I5 1S7mQP8u/B5O1PAeCMWfaf1uWB/VFFB82TetMcI1D8R6eQKmvIOI1ERFbEuh/R/B zL68i6qq36NvLkL5owrK6oq5S329PvY191GO9uxr7ce9RaQ/+zHnP0xlqYxhGJ5C G6nSMEzJGfIKiUdxgSbGxjwMpe9trnC644yeJpv3rQjM5LYwwtQ5tWSbc94CnKkY EB2hAbAUI68= =hba3 -----END PGP SIGNATURE-----