The IBM z/VM TCP/IP PENDINGCONNECTIONLIMIT statement must be properly configured.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-237927	SRG-OS-000142-GPOS-00071	IBMZ-VM-000740	SV-237927r858989_rule	2022-08-31	2

Description
DoS is a condition when a resource is not available for legitimate users. When this occurs, the organization either cannot accomplish its mission or must operate at degraded capacity. Managing excess capacity ensures that sufficient capacity is available to counter flooding attacks. Employing increased capacity and service redundancy may reduce the susceptibility to some DoS attacks. Managing excess capacity may include, for example, establishing selected usage priorities, quotas, or partitioning. The PENDINGCONNECTIONLIMIT statement defines the maximum number of half-open connections that are allowed at any given time. When a new half-open connection causes this limit to be exceeded, a random current half-open connection is dropped and a SynFlood denial-of-service attack is declared.

Description

DoS is a condition when a resource is not available for legitimate users. When this occurs, the organization either cannot accomplish its mission or must operate at degraded capacity. Managing excess capacity ensures that sufficient capacity is available to counter flooding attacks. Employing increased capacity and service redundancy may reduce the susceptibility to some DoS attacks. Managing excess capacity may include, for example, establishing selected usage priorities, quotas, or partitioning. The PENDINGCONNECTIONLIMIT statement defines the maximum number of half-open connections that are allowed at any given time. When a new half-open connection causes this limit to be exceeded, a random current half-open connection is dropped and a SynFlood denial-of-service attack is declared.

ℹ️ Check
Examine the "TCP/IP" configuration file. If there is no "PENDINGCONNECTIONLIMIT" statement, this is a finding.

✔️ Fix
Configure the "PENDINGCONNECTIONLIMIT" statement with a value that is less than the "TCBPOOLSIZE".