CVE-2026-18728 is an integer underflow vulnerability (CWE-191) in the iscsiuio component of open-iscsi, specifically during IPv4 DHCP parsing. This flaw allows an adjacent network attacker to cause a denial of service by sending a crafted IPv4/UDP DHCP reply that triggers an out-of-bounds read, crashing the iscsiuio process. The vulnerability requires the iscsiuio process to be actively handling IPv4 DHCP traffic and the attacker to be on the same local network segment. The issue is rated moderate severity with a CVSS 3.1 score of 6.5 (AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). No official patch is currently referenced in the advisory. Mitigation recommendations include restricting network access to iscsiuio interfaces, limiting DHCP/BOOTP traffic to trusted infrastructure via firewall rules, and considering static IP configuration to avoid DHCP usage. The vulnerability impacts availability by causing process crashes but does not affect confidentiality or integrity.

An attacker on the same local network segment can cause a denial of service by crashing the iscsiuio process through crafted DHCP replies. This results in loss of availability of the iscsiuio service on affected systems. There is no impact on confidentiality or integrity. Exploitation requires specific network conditions and vulnerable iscsiuio configuration, limiting the scope of impact.

No official patch or fix is currently confirmed. Mitigation involves restricting network access to iscsiuio-managed interfaces and configuring firewall rules to limit DHCP/BOOTP traffic to trusted infrastructure within the local broadcast domain. If feasible, reconfigure iscsiuio to use static IP addresses instead of IPv4 DHCP to reduce exposure. Changes to network configuration may require restarting the iscsiuio service. These mitigations reduce the risk of receiving crafted DHCP packets that trigger the vulnerability.