--- id: "CVE-2026-102551" kind: "vulnerability" aliases: ["CVE-2026-102551"] title: "Improper verification of the source of a communication channel in the IPv6 Router Advertisement handler in Amazon\u2026" severity: "critical" cvss: 9.2 epss: null exploited: false status: "open" category: "package" products: [] ecosystems: [] tags: ["amazon-freertos", "aws", "embedded", "freertos", "iot", "lab-disclosure", "package"] not_affected_if: ["fixed-version", "ipv4-only", "ipv6-disabled"] published_at: "2026-10-16T00:00:00+00:00" first_seen_at: "2026-10-23T21:57:13+00:00" updated_at: "2026-10-24T18:56:55+00:00" sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-102551", "first_seen_at": "2026-10-23T21:57:13+00:00"}, {"source": "lab", "url": "https://aws.amazon.com/security/security-bulletins/rss/2026-139-aws/", "first_seen_at": "2026-10-24T18:56:55+00:00"}] --- # Improper verification of the source of a communication channel in the IPv6 Router Advertisement handler in Amazon… Amazon FreeRTOS-Plus-TCP before V4.4.2 does not verify the source of IPv6 Router Advertisement messages. A remote attacker on the local network can send a crafted Router Advertisement to change a device's IPv6 default gateway, on-link prefix and address configuration, which can redirect or intercept its traffic. _Summary, check and fix written by a model from the sources; labelled as such._ ## How to check Check whether the firmware or application links FreeRTOS-Plus-TCP and find its version (V4.4.2 or later is fixed). ## Fix Upgrade FreeRTOS-Plus-TCP to V4.4.2 or later. ## Mitigated for you by - Team (workaround): covers Devices where ipconfigUSE_RA is set to ipconfigDISABLE, so Router Advertisements are not processed Limits: Does not apply where the device needs IPv6 RA-based autoconfiguration; ipconfigUSE_IPv6 can instead be disabled entirely Still: Set ipconfigUSE_RA to ipconfigDISABLE (or ipconfigUSE_IPv6 to ipconfigDISABLE) in FreeRTOSIPConfig.h until upgrading to V4.4.2 https://aws.amazon.com/security/security-bulletins/rss/2026-139-aws/ - Team (workaround): covers On-link Router Advertisement vector, via RA Guard and/or SEND deployed on the local link Limits: Does not address the off-link vector reachable during lease-renewal windows Still: Deploy RA Guard and/or SEND on the local link https://aws.amazon.com/security/security-bulletins/rss/2026-139-aws/ ## Timeline - 2026-10-23T21:57:13+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-102551 - 2026-10-24T18:56:55+00:00 lab https://aws.amazon.com/security/security-bulletins/rss/2026-139-aws/ — AWS: CVE-2026-102551 & CVE-2026-102552 - Issue with FreeRTOS-Plus-TCP ## Documents - [advisory] AWS: CVE-2026-102551 & CVE-2026-102552 - Issue with FreeRTOS-Plus-TCP https://aws.amazon.com/security/security-bulletins/rss/2026-139-aws/ ## From the sources CVE-2026-102551 & CVE-2026-102552 - Issue with FreeRTOS-Plus-TCP ### CVE-2026-102551 & CVE-2026-102552 - Issue with FreeRTOS-Plus-TCP Bulletin ID: 2026-139-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 10/16/2026 10:15 AM PDT Description: FreeRTOS-Plus-TCP is an open-source, thread-safe TCP/IP stack for the FreeRTOS kernel, distributed by Amazon for use on embedded and IoT devices. AWS identified two issues with FreeRTOS-Plus-TCP, affecting multiple versions. CVE-2026-102551: improper verification of the source of a communication channel in the IPv6 Router Advertisement handler. The handler does not fully validate that a received Router Advertisement originates from an on-link source before acting on it. Under certain conditions, a remote third-party might influence an endpoint's IPv6 gateway, prefix, and address configuration, potentially enabling interception of the device's IPv6 traffic. This issue is reachable in the library's default configuration, where ipconfigUSE_IPv6 and ipconfigUSE_RA are both enabled. CVE-2026-102552: improper verification of the source of a communication channel in the DNS resolver. The resolver does not fully validate that a DNS reply originates from the server that was queried before accepting it. Under certain conditions, a remote third-party might insert a chosen address into the device's DNS cache, potentially redirecting the device's subsequent connections for the affected name. Impacted versions: - CVE-2026-102551 (Router Advertisement): <= V4.4.1 - CVE-2026-102552 (DNS resolver): <= V4.4.1 Resolution: This issue has been addressed in FreeRTOS-Plus-TCP version V4.4.2. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes. For the DNS resolver issue, responder source-IP validation is provided as an opt-in option and is disabled by default; upgrading alone does not remediate it. To remediate, upgrade to V4.4.2 and enable ipconfigDNS_CHECK_REPLY_SOURCE_IP in FreeRTOSIPConfig.h. Workarounds: - CVE-2026-102551 (Router Advertisement): If upgrading is not immediately possible, disable IPv6 Router Advertisement processing by setting ipconfigUSE_RA to ipconfigDISABLE (or disable IPv6 entirely with ipconfigUSE_IPv6 = ipconfigDISABLE) in FreeRTOSIPConfig.h where the device does not require IPv6 RA-based autoconfiguration. On the network side, deploying RA Guard and/or SEND on the local link mitigates the on-link vector but does not address the off-link vector reachable during lease-renewal windows. - CVE-2026-102552 (DNS resolver): There is no configuration-only workaround on affected versions, because responder source-IP validation does not exist prior to V4.4.2. Where feasible, restricting the device to a trusted local resolver and protecting the local network path reduces unintended access to off-path reply forgery but does not eliminate the issue. References: - CVE-2026-102551 - CVE-2026-102552 - GHSA-pjq5-fqrr-g6pv - GHSA-h4fw-pv82-p7h5 Acknowledgement: We would like to thank Cipher / Causal Security for collaborating on this issue through the coordinated vulnerability disclosure process. Please email aws-security@amazon.com with any security questions or concerns. --- _Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_