CVE-2026-48490

Executive Summary

CVE-2026-48490 is a stack-based buffer overflow (CWE-120) in the ArduinoCore-avr platform, the source code and configuration files underlying Arduino AVR Boards. In versions prior to 1.8.8, concatenating floating-point values of sufficiently large magnitude onto an Arduino String object causes dtostrf() to write beyond a fixed-size stack buffer, resulting in memory corruption and denial of service, with a potential for arbitrary code execution on AVR-based boards under specific conditions. Any deployment using the affected library and processing attacker-influenceable float/double values is exposed, though exploitation requires a high degree of attack complexity.

Technical Analysis

The ArduinoCore-avr platform provides the core runtime and the String class for AVR-based Arduino boards. The vulnerability resides in the string-to-float conversion and concatenation path. When a floating-point value is appended to a String object via the String::concat(float) overload, the String::concat(double) overload, the String::operator+=() operator, or the + operator with a float/double operand, the implementation relies on the standard-library dtostrf() function to format the value into a character buffer.

Per NVD, dtostrf() writes into a fixed-size stack buffer. The size of that buffer is not scaled to the number of characters required to render extreme floating-point magnitudes. When a value "near the extremes of the float or double range" is supplied, the formatted representation exceeds the buffer capacity, and dtostrf() writes past the end of the stack-allocated region. This is the classic unbounded-copy stack overflow captured by CWE-120 (Buffer Copy without Checking Size of Input).

The relevant attack surface is any code path in which an externally influenced numeric value is converted to a string. Because the flaw lives in the string formatting layer rather than in network parsing, it can be reached from any input channel that ends in String concatenation of a float/double: serial command interfaces, firmware that echoes received values, sensor/telemetry aggregation from untrusted sources, or any application logic that forwards a parsed floating-point token into a String.

The core mechanism has two consequences:

1. Memory corruption — the overwrite damages adjacent stack memory. On AVR, this can corrupt saved registers, the return address, or other local variables, breaking control flow.
2. Denial of service — the most reliably attainable outcome is a crash or hang due to corrupted execution state.

The NVD description notes that, "under specific conditions," the corruption "could enable arbitrary code execution on AVR-based Arduino boards." This is a conditional consequence rather than a guaranteed outcome, and no further exploitation specifics are documented. The description does not enumerate the exact buffer size, the exact threshold magnitude, or the precise calling sequence; those details are not available from the provided data and are not speculated here.

Note on versioning: the vulnerable artifact is the ArduinoCore-avr Boards platform distributed via the Arduino IDE Boards Manager and the upstream repository. Consumers who pin older platform versions in build pipelines or CI images retain exposure even after the toolchain is updated.

Exploitation Scenarios

No public proof-of-concept, exploit code, or Nuclei template exists for CVE-2026-48490. The attack chain below is inferred strictly from the vulnerability class and the NVD description; no specific function beyond those named in NVD is assumed.

1. Reconnaissance / target identification. An attacker identifies a target AVR-based Arduino deployment that (a) runs an ArduinoCore-avr platform version prior to 1.8.8 and (b) exposes an input channel whose data ultimately reaches a String concatenation involving a float or double. Candidate channels include serial/USB command interfaces, network-connected shields (Ethernet/Wi-Fi) bridging parsed numeric input to application strings, and any telemetry/logging path that forwards remote numeric values.

2. Triggering the flaw class. The attacker supplies a floating-point value at or near the extreme of the representable float/double range through the identified input channel. Application code parses the token into a float or double and appends it to a String object using String::concat(float), String::concat(double), String::operator+=(), or the + operator with a float/double operand. The resulting formatted representation overruns the fixed-size stack buffer used by dtostrf(), producing an out-of-bounds write (CWE-120).

3. Payload/execution method. At the vulnerability-class level, the attacker seeks to control the bytes that spill past the buffer boundary and thereby influence adjacent stack contents. Because the overflowed content is derived from a numeric text representation, the attacker's control over write contents is constrained by the formatting logic; crafting a controlled overwrite is a high-complexity effort and, per NVD, arbitrary code execution is achievable only "under specific conditions." Without a public PoC, the precise byte-level construction is not documented.

4. Post-exploitation impact. The immediate, reliable impact is memory corruption leading to denial of service — the board crashes, resets, or hangs, interrupting any physical process it controls. In scenarios where the overwrite is successfully shaped, the potential exists for arbitrary code execution on the AVR microcontroller, which would give the attacker control over the device's firmware-level behavior. The NVD description does not characterize lateral movement or persistence, and none should be assumed.

Impact Assessment

• Confidentiality (Low): Stack memory contents may be exposed or corrupted; no direct data-exfiltration primitive is documented.
• Integrity (Low): Memory corruption alters program state and can modify control-flow data.
• Availability (High): Denial of service via crash/hang is the most attainable and documented outcome.
• Attack Vector (Network): Reachable over any channel that delivers attacker-controlled numeric input to the affected API.
• Attack Complexity (High): Exploitation requires a value at the extremes of the float/double range and a code path that concatenates it; reliable code execution is conditional.
• Privileges Required (None) / User Interaction (None): No authentication or user action is assumed to reach the vulnerable conversion path.

Blast radius. The impacted population is not conventional enterprise IT. It is embedded and OT/ICS-adjacent: industrial controllers, laboratory instrumentation, educational and hobbyist platforms, and any product embedding the ArduinoCore-avr platform. Because AVR boards frequently sit at the boundary between digital control and physical actuation, a denial-of-service condition can translate into physical-process disruption. The absence of a CVSS score from an authoritative source, and the lack of an EPSS score, mean prioritization must rely on exposure and reachability rather than on a vendor-assigned severity.

Detection Guidance

Detection of CVE-2026-48490 is fundamentally difficult at the network layer because it is a memory-safety flaw in local string formatting, not a protocol-level bug. The rules below target anomalous numeric payloads, affected platform versions in build artifacts, and firmware crash/reset patterns. Because no exploit traffic has been observed, these are heuristic detections and should be tuned.

Sigma Rule

title: Potential ArduinoCore-avr String Float Overflow Attempt (CVE-2026-48490)
id: 8f3c1a72-4b9e-4d21-9c77-2a6f0e5d1b34
status: experimental
description: Detects input containing extreme-magnitude floating point values directed at systems likely to concatenate them onto an Arduino String object (CVE-2026-48490).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-48490
author: valtersit.com
date: 2026-06-06
logsource:
  category: application
  product: arduino
detection:
  selection_extreme:
    payload|re: '(?i)(3\.4\d{30,}e\+38|[0-9]\.\d{300,}e\+[0-9]{3,})'
  selection_api:
    message|contains:
      - 'String::concat'
      - 'String::operator+='
  condition: selection_extreme or selection_api
falsepositives:
  - Legitimate scientific/telemetry data with very long precision
level: medium

YARA Rule

rule CVE_2026_48490_ArduinoCore_avr_String_Overflow
{
    meta:
        description = "Detects ArduinoCore-avr platform artifacts predating the 1.8.8 fix and float/double String concatenation patterns related to CVE-2026-48490"
        author = "valtersit.com"
        date = "2026-06-06"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-48490"
        cve = "CVE-2026-48490"
    strings:
        $dtostrf = "dtostrf" ascii
        $concat_f = "concat(float" ascii
        $concat_d = "concat(double" ascii
        $op_add = "operator+=" ascii
        $ver_old = "1.8.7" ascii
        $ver_old2 = "1.8.6" ascii
        $ver_old3 = "1.8.5" ascii
    condition:
        $dtostrf and (any of ($concat_f, $concat_d, $op_add)) and any of ($ver_old*)
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2026-48490 ArduinoCore-avr extreme float value input (potential String concat overflow)"; flow:to_server,established; content:"e+38"; nocase; pcre:"/(?:[0-9]\.\d{40,}e\+3[0-9])/"; threshold:type both, track by_src, count 5, seconds 60; classtype:attempted-dos; reference:cve,2026-48490; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-48490; sid:2026484900; rev:1;)

Elastic Detection

sequence by host.id with maxspan=30s
  [process where process.name == "arduino-builder" and process.args : "*arduino*"]
  [network where network.direction == "inbound" and
     process.name : ("python*","node*","java*") and
     string(network.payload) regex~ ".*[0-9]\\.[0-9]{40,}e\\+3[0-9].*"]

Splunk SPL Query

index=embedded OR index=iot sourcetype=arduino:serial OR sourcetype=arduino:net
| where match(payload, "(?i)[0-9]\.\d{40,}e\+3[0-9]")
| stats count values(payload) as sample_values dc(src_ip) as unique_sources by host
| where count > 3
| table host count unique_sources sample_values

Wazuh OSSEC Rule

<group name="arduino,cve-2026-48490,">
  <rule id="202648" level="10">
    <decoded_as>json</decoded_as>
    <field name="payload">\.\d{40,}e\+3[0-9]</field>
    <description>CVE-2026-48490: Extreme-magnitude floating point input detected; potential Arduino String concatenation buffer overflow.</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>buffer_overflow,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). The NVD description states that "the fix is included starting from the 1.8.8 release," but no vendor advisory, commit reference, or release artifact has been confirmed by tracked sources, so treat this as a stated fix version rather than a verified patched build.

1. Immediate mitigations

   • Audit firmware for any code path invoking String::concat(float), String::concat(double), String::operator+=(), or the + operator with a float/double operand on values derived from untrusted input.
   • Validate and clamp floating-point input before it reaches string conversion; reject values whose magnitude exceeds an application-appropriate bound.
   • Prefer formatting floats into a caller-supplied, size-checked character buffer rather than unbounded String concatenation.
   • Isolate or rate-limit untrusted input channels (serial, network shields) that feed numeric values into logging or echo logic.
   • Apply watchdogs and fail-safe resets to reduce the physical impact of a crash/hang.

2. Patch/upgrade steps

   • Upgrade the Arduino AVR Boards platform to version 1.8.8 or later via the Arduino IDE Boards Manager.
   • Update pinned platform versions and cached build images in CI/CD to eliminate the vulnerable artifact.
   • Rebuild and re-flash all firmware produced from the affected platform version.

3. Long-term hardening

   • Add static analysis (SAST) and fuzzing for numeric-formatting paths in embedded firmware to catch unbounded copies pre-deployment.
   • Adopt memory-safe string-formatting practices for untrusted numeric input.
   • Maintain an SBOM of embedded platform/library versions across the fleet and monitor upstream releases for this class of defect.

References

• NVD — CVE-2026-48490: https://nvd.nist.gov/vuln/detail/CVE-2026-48490
• ArduinoCore-avr upstream project (Arduino AVR Boards platform): https://github.com/arduino/ArduinoCore-avr
• Arduino Boards Manager documentation (platform upgrade path to 1.8.8+): https://www.arduino.cc/en/software
• CWE-120 — Buffer Copy without Checking Size of Input: https://cwe.mitre.org/data/definitions/120.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/

Exploit-in-the-wild / threat actor evidence: None. CVE-2026-48490 is not listed in CISA KEV, has no public PoC or exploit code, no Nuclei template, and no known threat actor campaigns as of this report. EPSS has not yet scored this CVE; no probabilistic exploitation value is available and none is asserted here.