EUVD-2026-26276Severity by source
CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
AV:A because only link-local adjacent attackers can reach the reply handler; A:H for device crash; no C or I impact; PR:N confirmed by CVSS 4.0 input.
Primary rating from NVD.
CVSS VectorNVD
Lifecycle Timeline
6DescriptionCVE.org
Integer underflow in the ICMP and ICMPv6 echo reply handlers in FreeRTOS-Plus-TCP before V4.4.1 and V4.2.6 allows an adjacent network user 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 of up to approximately 65KB.
To mitigate this issue, users should upgrade to the fixed version when available.
AnalysisAI
Integer underflow in FreeRTOS-Plus-TCP's ICMP and ICMPv6 echo reply handlers enables an adjacent network attacker to crash any affected embedded or IoT device that has outgoing ping support enabled. The flaw spans two active release branches - 4.0.0 through 4.2.5 and 4.3.0 through 4.4.0 - and can trigger a heap out-of-bounds read of up to approximately 65KB, resulting in device denial of service. No public exploit has been identified and EPSS sits at 0.01% (3rd percentile), but the impact on resource-constrained embedded devices can be severe given their limited fault tolerance.
Technical ContextAI
FreeRTOS-Plus-TCP (CPE: cpe:2.3:a:aws:freertos-plus-tcp) is the AWS-maintained TCP/IP networking stack add-on for the FreeRTOS real-time operating system, widely used in embedded and IoT firmware. The root cause is CWE-191 (Integer Underflow): when the stack receives an ICMP or ICMPv6 echo reply in response to an outgoing ping, the reply handler subtracts header byte counts from the packet length field without first verifying that the field value is large enough to accommodate those subtractions. On platforms using unsigned integer arithmetic - standard for embedded C - this produces a very large positive result rather than a negative one. That inflated value is then used to bound a heap read, allowing the stack to access up to roughly 65KB beyond the allocated packet buffer, causing a crash. The bug is confined to the echo reply path (outgoing ping), not inbound ping handling.
RemediationAI
Vendor-released patches are confirmed available: upgrade to FreeRTOS-Plus-TCP V4.4.1 for the 4.3.x branch (https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/releases/tag/V4.4.1) or V4.2.6 for the 4.0.x/4.2.x branch (https://github.com/FreeRTOS/FreeRTOS-Plus-TCP/releases/tag/V4.2.6). The AWS security bulletin at https://aws.amazon.com/security/security-bulletins/2026-021-aws/ provides additional vendor guidance. If an immediate firmware rebuild is not feasible, the most effective compensating control is to disable outgoing ping support in the FreeRTOS-Plus-TCP configuration; this eliminates the attack surface entirely since the vulnerable echo reply handler is only reachable after the device itself initiates a ping - disabling this feature has no impact on normal TCP/UDP application traffic. As a secondary control, VLAN or network segmentation to isolate FreeRTOS devices from untrusted adjacent hosts reduces exploitability given the AV:A constraint, though this does not fix the underlying flaw.
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Same weakness CWE-191 – Integer Underflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today