EUVD-2026-36661
GHSA-6f53-f2m4-6j2h
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N/E:P/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:Y/R:X/V:X/RE:X/U:X
Single crafted Modbus/TCP frame on port 502 with no auth or interaction (AV:N/AC:L/PR:N/UI:N); reliable DoS gives A:H while conditional one-byte leak and unintended writes give C:L/I:L.
Primary rating from Vendor (TuranSec).
CVSS VectorVendor: TuranSec
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N/E:P/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:Y/R:X/V:X/RE:X/U:X
Lifecycle Timeline
1DescriptionCVE.org
nanoMODBUS through v1.23.0 contains an off-by-one buffer overflow in the recv_msg_header() function of the Modbus/TCP server that allows remote unauthenticated attackers to write one attacker-controlled byte past the end of the 260-byte receive buffer by sending a crafted MBAP frame whose Length field is set to 255. The overflow corrupts the adjacent buffer-index field of the nanoMODBUS state structure, resulting in denial of service through invalid memory accesses and, on bare-metal and RTOS targets without memory protection, one-byte information disclosure and writes to unintended register addresses on the Write Multiple Registers (FC16) handler path.
AnalysisAI
Off-by-one buffer overflow in nanoMODBUS through v1.23.0 lets remote unauthenticated attackers write one attacker-controlled byte past a 260-byte receive buffer in the Modbus/TCP server's recv_msg_header() function. The corruption of the adjacent buffer-index field can cause denial of service on all targets and, on bare-metal/RTOS deployments without memory protection, leak one byte of memory and trigger unintended writes through the Write Multiple Registers (FC16) handler. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The target must be running nanoMODBUS ≤ v1.23.0 compiled with the Modbus/TCP server role and reachable on TCP/502 from the attacker; no authentication, user interaction, or non-default configuration is required because Modbus/TCP has no native auth. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The provided CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N, VA:H, VC:L/VI:L) accurately reflects a remote, unauthenticated, low-complexity reach with high availability impact and low confidentiality/integrity impact, consistent with the description's primary DoS outcome and conditional info-disclosure/unintended-write secondaries. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker with TCP reach to a device's Modbus/TCP port 502 opens a connection and sends a single MBAP frame whose 16-bit Length field is set to 255, triggering the off-by-one write at the end of the 260-byte receive buffer and corrupting the state machine's buffer-index. On a Linux target the service crashes (DoS of the industrial endpoint); on an RTOS or bare-metal PLC, the attacker follows up with a Write Multiple Registers (FC16) request that, due to the corrupted index, lands at an unintended register address - potentially altering a setpoint or coil that controls a physical process. … |
| Remediation | No vendor-released patch identified at time of analysis; monitor the upstream repository at https://github.com/debevv/nanoMODBUS for a release succeeding v1.23.0 and rebuild/reflash firmware once a fixed tag is published. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: inventory all systems running nanoMODBUS and classify by deployment type (bare-metal, RTOS, or protected OS) and network criticality. …
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External POC / Exploit Code
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