CVE-2026-48490 Overview
CVE-2026-48490 is a stack-based buffer overflow [CWE-120] in ArduinoCore-avr, the source code and configuration files of the Arduino AVR Boards platform. Versions prior to 1.8.8 mishandle floating-point-to-string conversion when concatenating values onto an Arduino String object. Passing float or double values near the extremes of their representable range to String::concat(float), String::concat(double), String::operator+=(), or the + operator with a float/double operand causes dtostrf() to write past a fixed-size stack buffer. The result is memory corruption and denial of service on AVR-based Arduino boards, with the potential for arbitrary code execution under specific conditions.
Critical Impact
Attackers who can influence floating-point input to a vulnerable String concatenation can corrupt stack memory on AVR-based Arduino boards, causing denial of service and, in specific conditions, arbitrary code execution.
Affected Products
- Arduino ArduinoCore-avr versions prior to 1.8.8
- Arduino AVR Boards platform (AVR-based Arduino boards)
- Sketches using String::concat(float), String::concat(double), String::operator+=(), or the + operator with float/double operands
Discovery Timeline
- 2026-09-11 - CVE-2026-48490 published to NVD
- 2026-09-14 - Last updated in NVD database
Technical Details for CVE-2026-48490
Vulnerability Analysis
The vulnerability lives in the Arduino core String class implementation for AVR targets. When a sketch appends a floating-point value to a String, the library converts the number to text using dtostrf() and stores the result in a fixed-size stack buffer before appending. The buffer is sized for typical values and does not account for very large magnitudes, where dtostrf() produces long integer portions plus fractional digits, sign, and terminator. Values close to the maximum representable float or double therefore produce output longer than the buffer can hold. dtostrf() writes the full converted string regardless, overrunning the stack frame and corrupting adjacent data including saved registers and return addresses.
On AVR microcontrollers, which lack memory protection and address-space layout randomization, deterministic stack layout makes the corruption predictable. An attacker who can supply a controlled float or double to a vulnerable concatenation path can crash the device or, in specific conditions, redirect execution.
Root Cause
The root cause is missing bounds validation on the destination buffer used by dtostrf() inside the String floating-point concatenation helpers. The buffer is statically sized for common values and does not scale with the magnitude of the input. See the GitHub Pull Request Changes for the code-level fix.
Attack Vector
Exploitation requires that an AVR-based Arduino sketch concatenate an attacker-influenced float or double onto a String. Input paths include serial data parsed with parseFloat(), network payloads from Ethernet or Wi-Fi shields, sensor telemetry, and MQTT or HTTP request bodies. Because the CVSS vector marks the attack vector as network, remote exploitation is in scope wherever the device exposes a network interface that feeds untrusted floats into vulnerable string operations. See the GitHub Security Advisory GHSA-fhp2-f8hw-mgpj for advisory details.
Detection Methods for CVE-2026-48490
Indicators of Compromise
- Unexpected resets, watchdog reboots, or hangs on AVR-based Arduino devices immediately after processing floating-point input.
- Serial output showing truncated or corrupted String contents following concatenation of large float or double values.
- Firmware execution diverging from expected control flow after receiving numeric payloads over serial, network, or radio interfaces.
Detection Strategies
- Audit sketch source code for calls to String::concat(float), String::concat(double), String::operator+=(), and the + operator applied to float or double operands.
- Verify the installed ArduinoCore-avr version against 1.8.8 or later using the Arduino IDE Boards Manager or the boards.txt metadata.
- Fuzz exposed interfaces with float values near FLT_MAX, FLT_MIN, DBL_MAX, and DBL_MIN to reproduce crashes attributable to the overflow.
Monitoring Recommendations
- Monitor upstream systems that forward telemetry from AVR devices for repeated device reboots or communication gaps.
- Log and alert on malformed numeric fields in application-layer protocols feeding embedded endpoints.
- Track ArduinoCore-avr versions across firmware build pipelines and CI artifacts to catch downgrades or unpatched builds.
How to Mitigate CVE-2026-48490
Immediate Actions Required
- Update ArduinoCore-avr to version 1.8.8 or later via the Arduino IDE Boards Manager and rebuild all affected firmware.
- Redeploy patched firmware to every AVR-based Arduino board that accepts floating-point input from external sources.
- Validate and clamp float and double inputs at the application layer before passing them to String concatenation.
Patch Information
The fix is included starting with the GitHub Release v1.8.8 of ArduinoCore-avr. The corresponding code change is documented in the GitHub Pull Request Changes, and the coordinated advisory is published as GHSA-fhp2-f8hw-mgpj.
Workarounds
- Convert floating-point values to strings manually with a caller-owned buffer sized for the maximum expected magnitude before appending to String.
- Reject or saturate incoming float and double values that exceed a safe application-defined range prior to any concatenation.
- Prefer fixed-point or integer representations for network-facing numeric fields on constrained AVR targets until firmware is patched.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
