Issue with FreeRTOS-Plus-TCP - MAC Address Validation Bypass and ICMP Echo Reply Integer Underflow
Bulletin ID: 2026-021-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 2026/04/29 12:00 PM PDT Description: FreeRTOS-Plus-TCP is a scalable, open source, and thread-safe TCP/IP stack for FreeRTOS. - CVE-2026-7422: Insufficient packet validation in the IPv4 and IPv6 receive paths allows an adjacent network device to send a packet that bypasses checksum and minimum-size validation by spoofing the Ethernet source MAC address to match one of the target device's own registered endpoints. - CVE-2026-7423: Integer underflow in the ICMP and ICMPv6 echo reply handlers allows an adjacent network device to cause a denial of service (device crash) when outgoing ping support is enabled, because header sizes are subtracted from a packet length field without validating the field is large enough, resulting in a heap out-of-bounds read. Impacted versions: >=V4.0.0 AND <=V4.2.5, >=V4.3.0 AND <=V4.4.0 Please refer to the article below for the most up-to-date and complete information related to this AWS Security Bulletin.
CSIRTS triage
- What
- Insufficient packet validation and integer underflow issues could allow for MAC address validation bypass and denial of service.
- Who is affected
- Users of FreeRTOS-Plus-TCP within the specified version range.
- Urgency
- Remediation is urgent due to the potential for denial of service and privilege escalation.
- Action
- Upgrade to a version outside the specified range.
AI-assisted analysis generated from the source advisory — verify against the original.
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Details
Original advisory: https://aws.amazon.com/security/security-bulletins/rss/2026-021-aws/
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2026-74220.18% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 7% of all scored CVEs.
- Low exploitation riskCVE-2026-74230.22% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 13% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-7422 | coverage & exploitation status | NVD · CVE.org |
| CVE-2026-7423 | coverage & exploitation status | NVD · CVE.org |
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