CVE-2021-31378

In broadband environments, including but not limited to Enhanced Subscriber Management, (CHAP, PPP, DHCP, etc.), on Juniper Networks Junos OS devices where RADIUS servers are configured for managing subscriber access and a subscriber is logged in and then requests to logout, the subscriber may be forced into a Terminating state by an attacker who is able to send spoofed messages appearing to originate from trusted RADIUS server(s) destined to the device in response to the subscribers request. These spoofed messages cause the Junos OS General Authentication Service (authd) daemon to force the broadband subscriber into this Terminating state which the subscriber will not recover from thereby causing a Denial of Service (DoS) to the endpoint device. Once in the Terminating state, the endpoint subscriber will no longer be able to access the network. Restarting the authd daemon on the Junos OS device will temporarily clear the subscribers out of the Terminating state. As long as the attacker continues to send these spoofed packets and subscribers request to be logged out, the subscribers will be returned to the Terminating state thereby creating a persistent Denial of Service to the subscriber. An indicator of compromise may be seen by displaying the output of show subscribers summary. The presence of subscribers in the Terminating state may indicate the issue is occurring. This issue affects: Juniper Networks Junos OS 17.3 versions prior to 17.3R3-S12; 17.4 versions prior to 17.4R3-S5; 18.1 versions prior to 18.1R3-S13; 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R2-S8, 18.4R3-S9; 19.1 versions prior to 19.1R3-S6; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S3; 19.4 versions prior to 19.4R1-S4, 19.4R1-S4, 19.4R3-S3; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R3-S1; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R2. This issue does not affect: Juniper Networks Junos OS 12.3 version 12.3R1 and later versions; 15.1 version 15.1R1 and later versions.

Weakness

The product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.

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, languages such as Java, Ruby, and Lisp perform automatic garbage collection that releases memory for objects that have been deallocated.
• Use resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems.
• When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users.
• Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/469.html

References

• https://kb.juniper.net/JSA11246
• https://www.juniper.net/documentation/us/en/software/junos/subscriber-mgmt-sessions/topics/topic-map/general-authentication-service-events-tracing.html