CVE-2026-51273: ESP32-audioI2S Buffer Overflow Vulnerability

CVE-2026-51273 Overview

CVE-2026-51273 is a heap-based buffer overflow in the schreibfaul1 ESP32-audioI2S library version 3.4.5. The flaw exists in the showID3Tag() function within the embedded audio streaming library. The function reads untrusted ID3 tag values from audio files and passes them to an unbounded appendf() call that writes formatted strings into a ps_ptr heap buffer without length validation. An attacker who supplies a crafted audio file can trigger memory corruption on the ESP32 device. The weakness is classified as [CWE-122] Heap-Based Buffer Overflow.

Critical Impact
Successful exploitation allows arbitrary code execution, memory disclosure, device crash, or privilege escalation on ESP32 devices that process attacker-supplied audio streams.

Affected Products

schreibfaul1 ESP32-audioI2S version 3.4.5
ESP32-based embedded devices integrating the ESP32-audioI2S library
Audio streaming applications that invoke showID3Tag() during ID3 metadata parsing

Discovery Timeline

2026-07-28 - CVE-2026-51273 published to NVD
2026-07-28 - Last updated in NVD database

Technical Details for CVE-2026-51273

Vulnerability Analysis

The ESP32-audioI2S library provides audio decoding and I2S streaming for ESP32 microcontrollers. During playback, the library parses ID3 metadata tags embedded in MP3 and related audio containers. The showID3Tag() function reads tag values directly from file input and forwards them to an internal appendf() helper that formats the data into a dynamically allocated ps_ptr heap buffer.

The formatting call does not enforce an upper bound on the length of the incoming tag value. When the tag exceeds the allocated buffer capacity, appendf() writes past the end of the heap allocation. This corrupts adjacent heap metadata and adjacent objects on the ESP32 heap, which shares a flat address space with executable code on many firmware configurations.

Root Cause

The root cause is missing length validation on user-controlled input before a formatted write into a fixed-capacity heap buffer. The appendf() helper trusts the caller to bound the source data, and showID3Tag() never verifies the tag length against the destination allocation. This is a classic [CWE-122] pattern in which parser code treats file metadata as trusted.

Attack Vector

Exploitation requires the target device to load a malicious audio file. An attacker crafts an audio file with an oversized ID3 tag value and delivers it through any input path the firmware accepts, such as an SD card, an HTTP stream, or a Bluetooth transfer. User interaction is required to initiate playback. Once parsed, the overflow corrupts heap state and can be steered toward arbitrary code execution, memory disclosure, or a denial-of-service reboot.

No verified proof-of-concept code is published. Refer to the GitHub CVE-2026-51273 Advisory and the ESP32-audioI2S source for the vulnerable code paths.

Detection Methods for CVE-2026-51273

Indicators of Compromise

Unexpected ESP32 device reboots or watchdog resets during audio playback
Corrupted heap allocator diagnostics in serial console logs referencing ps_ptr
Audio files containing ID3 tag fields with abnormally long string values
Firmware crash dumps pointing to showID3Tag() or appendf() frames

Detection Strategies

Scan audio content repositories for ID3 tags exceeding conventional length limits before delivery to devices
Instrument firmware builds with heap canaries or ASAN-equivalent tooling to catch overflow attempts during testing
Correlate device telemetry showing repeated crashes with the specific audio file loaded prior to failure

Monitoring Recommendations

Collect ESP32 serial and telemetry logs into a centralized store and alert on repeated crash signatures in Audio.cpp
Monitor file transfer channels feeding audio content to embedded devices for anomalous MP3 metadata sizes
Track firmware version inventory to identify devices still running ESP32-audioI2S 3.4.5

How to Mitigate CVE-2026-51273

Immediate Actions Required

Identify all ESP32 firmware images that link against ESP32-audioI2S 3.4.5 and mark them for rebuild
Restrict audio input sources to trusted origins until a patched library is deployed
Disable ID3 tag processing in firmware where the metadata is not required for the application

Patch Information

At time of publication, no fixed release is listed in the referenced advisories. Monitor the ESP32-audioI2S repository for an updated version that adds length validation to showID3Tag() and rebuild firmware once available.

Workarounds

Pre-filter audio files on a trusted host and strip or truncate ID3 tag fields before transfer to the device
Modify local forks of Audio.cpp to enforce a maximum length check on ID3 tag values before calling appendf()
Isolate audio-processing devices on a segmented network to limit the delivery paths for malicious files

bash

# Configuration example: strip ID3 tags from MP3 files before deploying to ESP32 devices
find ./audio_content -name '*.mp3' -exec id3v2 --delete-all {} \;