# CVE-2026-18727: Open-iscsi: open-iscsi: integer underflow in iscsiuio dhcpv6 parsing

CVE-2026-18727 is fixed in 9 products on 1 platform, first by DEBIAN-CVE-2026-18727, released August 12, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-18727
- Priority: Routine
- CVSS: 6.5 (Moderate)
- EPSS: 0.0029
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Aug 12, 2026
- Weakness: Integer Underflow (Wrap or Wraparound)
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-18727

## Description

A flaw was found in open-iscsi's iscsiuio component. This vulnerability involves an integer underflow and out-of-bounds read during Dynamic Host Configuration Protocol for IPv6 (DHCPv6) packet parsing. Specifically, crafted DHCPv6 Advertise traffic with a short User Datagram Protocol (UDP) length can cause the DHCPv6 payload length to underflow. An unauthenticated attacker on an adjacent network segment can exploit this by sending specially crafted IPv6 UDP traffic while the client is in an active DHCPv6 exchange, leading to a denial of service due to a process crash or service disruption.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | iscsi-initiator-utils amzn 2023 | 6.2.1.4-10.git2a8f9d8.amzn2023.0.4 | [ALAS2023-2026-2120](https://patchblox.com/security/data/fix/linux/alas2023-2026-2120.md) | Aug 31, 2026 |
| Linux | iscsi-initiator-utils-debuginfo amzn 2023 | 6.2.1.4-10.git2a8f9d8.amzn2023.0.4 | [ALAS2023-2026-2120](https://patchblox.com/security/data/fix/linux/alas2023-2026-2120.md) | Aug 31, 2026 |
| Linux | iscsi-initiator-utils-debugsource amzn 2023 | 6.2.1.4-10.git2a8f9d8.amzn2023.0.4 | [ALAS2023-2026-2120](https://patchblox.com/security/data/fix/linux/alas2023-2026-2120.md) | Aug 31, 2026 |
| Linux | iscsi-initiator-utils-devel amzn 2023 | 6.2.1.4-10.git2a8f9d8.amzn2023.0.4 | [ALAS2023-2026-2120](https://patchblox.com/security/data/fix/linux/alas2023-2026-2120.md) | Aug 31, 2026 |
| Linux | iscsi-initiator-utils-iscsiuio amzn 2023 | 6.2.1.4-10.git2a8f9d8.amzn2023.0.4 | [ALAS2023-2026-2120](https://patchblox.com/security/data/fix/linux/alas2023-2026-2120.md) | Aug 31, 2026 |
| Linux | iscsi-initiator-utils-iscsiuio-debuginfo amzn 2023 | 6.2.1.4-10.git2a8f9d8.amzn2023.0.4 | [ALAS2023-2026-2120](https://patchblox.com/security/data/fix/linux/alas2023-2026-2120.md) | Aug 31, 2026 |
| Linux | open-iscsi Debian 12.15 (bookworm) | 2.1.8-1+deb12u1 | [DEBIAN-CVE-2026-18727](https://patchblox.com/security/data/fix/linux/debian-cve-2026-18727.md) | Aug 12, 2026 |
| Linux | open-iscsi Debian 14 | 2.1.13-1 | [DEBIAN-CVE-2026-18727](https://patchblox.com/security/data/fix/linux/debian-cve-2026-18727.md) | Aug 12, 2026 |
| Linux | python3-iscsi-initiator-utils amzn 2023 | 6.2.1.4-10.git2a8f9d8.amzn2023.0.4 | [ALAS2023-2026-2120](https://patchblox.com/security/data/fix/linux/alas2023-2026-2120.md) | Aug 31, 2026 |
| Linux | python3-iscsi-initiator-utils-debuginfo amzn 2023 | 6.2.1.4-10.git2a8f9d8.amzn2023.0.4 | [ALAS2023-2026-2120](https://patchblox.com/security/data/fix/linux/alas2023-2026-2120.md) | Aug 31, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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