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CVE-2026-48490: ArduinoCore-AVR: Stack-Based Buffer Overflow in String float/double concatenation handler

• Severity: medium (CVSS 6.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-11 · updated 2026-09-30
• Weakness: CWE-120

Description

ArduinoCore-avr contains the source code and configuration files of the Arduino AVR Boards platform. A vulnerability in versions prior to 1.8.8 allows an attacker to trigger a stack-based buffer overflow when concatenating floating-point values of sufficiently large magnitude onto an Arduino String object. By passing values near the extremes of the float or double range to `String::concat(float)`, `String::concat(double)`, `String::operator+=()`, or the `+` operator with a float/double operand, `dtostrf()` writes beyond the fixed-size stack buffer, causing memory corruption and denial of service. Under specific conditions, this could enable arbitrary code execution on AVR-based Arduino boards. The fix is included starting from the `1.8.8 `release.

Affected products

• ArduinoCore-avr: before 1.8.8

References

• https://github.com/arduino/ArduinoCore-avr/pull/622/changes/9492e146880d2b05d9cb9191f1bfb2c872a48404
• https://github.com/arduino/ArduinoCore-avr/releases/tag/1.8.8
• https://github.com/arduino/ArduinoCore-avr/security/advisories/GHSA-fhp2-f8hw-mgpj

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