CVE-2019-1840

A vulnerability in the DHCPv6 input packet processor of Cisco Prime Network Registrar could allow an unauthenticated, remote attacker to restart the server and cause a denial of service (DoS) condition on the affected system. The vulnerability is due to incomplete user-supplied input validation when a custom extension attempts to change a DHCPv6 packet received by the application. An attacker could exploit this vulnerability by sending malformed DHCPv6 packets to the application. An exploit could allow the attacker to trigger a restart of the service which, if exploited repeatedly, might lead to a DoS condition. This vulnerability can only be exploited if the administrator of the server has previously installed custom extensions that attempt to modify the packet details before the packet has been processed. Note: Although the CVSS score matches a High SIR, this has been lowered to Medium because this condition will only affect an application that has customer-developed extensions that will attempt to modify packet parameters before the packet has been completely sanitized. If packet modification in a custom extension happens after the packet has been sanitized, the application will not be affected by this vulnerability. Software versions prior to 8.3(7) and 9.1(2) are affected.

Weakness

The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, in Java, if the programmer does not explicitly initialize a variable, then the code could produce a compile-time error (if the variable is local) or automatically initialize the variable to the default value for the variable’s type. In Perl, if explicit initialization is not performed, then a default value of undef is assigned, which is interpreted as 0, false, or an equivalent value depending on the context in which the variable is accessed.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190417-pnr-dos
• http://www.securityfocus.com/bid/108033