Cisco ASA 9.3(1.50)/9.3(2.100)/9.3(3)/9.4(1) uRPF Validation Firewall input validation

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CTI Interest Score
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A vulnerability has been found in Cisco ASA 9.3(1.50)/9.3(2.100)/9.3(3)/9.4(1) (Firewall Software) and classified as critical. Affected by this vulnerability is an unknown functionality of the component uRPF Validation. The manipulation with an unknown input leads to a input validation vulnerability (Firewall). The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect confidentiality, integrity, and availability.

The weakness was released 08/12/2015 with Cisco as 40440 / CSCuv60724 as confirmed vulnerability alert (Website). It is possible to read the advisory at This vulnerability is known as CVE-2015-4321 since 06/04/2015. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 06/09/2022). The advisory points out:

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.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at X-Force (105519). Entries connected to this vulnerability are available at VDB-139665, VDB-139666, VDB-139667 and VDB-142839.








  • end of life (old version)

CPE 2.3info

CPE 2.2info


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VulDB Meta Base Score: 7.3
VulDB Meta Temp Score: 6.7

VulDB Base Score: 7.3
VulDB Temp Score: 6.7
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Name: Firewall
Class: Input validation / Firewall

Local: No
Remote: Yes

Availability: 🔍
Status: Unproven

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Current Price Estimation: 🔍


OpenVAS ID: 800316
OpenVAS Name: Cisco ASA uRFP Bypass Vulnerability
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Threat Intelligenceinfo

Interest: 🔍
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Recommended: no mitigation known
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0-Day Time: 🔍


06/04/2015 🔍
08/12/2015 +69 days 🔍
08/12/2015 +0 days 🔍
08/12/2015 +0 days 🔍
08/13/2015 +1 days 🔍
08/13/2015 +0 days 🔍
08/16/2015 +3 days 🔍
08/20/2015 +4 days 🔍
06/09/2022 +2485 days 🔍



Advisory: 40440 / CSCuv60724
Organization: Cisco
Status: Confirmed

CVE: CVE-2015-4321 (🔍)
X-Force: 105519 - Cisco Adaptive Security Appliance security bypass
SecurityTracker: 1033265 - Cisco ASA Lets Remote Users Bypass uRPF Validation on the Target System
Vulnerability Center: 51971 - Cisco Adaptive Security Appliance (ASA) Remote Security Bypass via Crafted IP Packets, Medium
SecurityFocus: 76325 - Cisco Adaptive Security Appliance Software CVE-2015-4321 Security Bypass Vulnerability

See also: 🔍


Created: 08/13/2015 10:34 AM
Updated: 06/09/2022 11:31 AM
Changes: 08/13/2015 10:34 AM (60), 10/14/2017 11:30 AM (14), 06/09/2022 11:31 AM (3)
Complete: 🔍
Cache ID: 34:C44:40


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