CVE-2026-19395: Qt for MCUs Text Element DoS Vulnerability

CVE-2026-19395 Overview

CVE-2026-19395 affects Qt for MCUs, the Qt framework variant designed for microcontroller-based embedded devices. A Text element that renders styled text halts the device when an <img> tag contains an attribute with an empty value. The text parser forwards the empty value to an internal check that only accepts non-empty values, triggering the default error handler which stops execution.

Critical Impact
Remote attackers can trigger a denial of service on affected microcontroller devices by supplying crafted styled text containing an <img> tag with an empty attribute value, halting the device without authentication or user interaction.

Affected Products

Qt for MCUs (styled Text element rendering path)
Embedded microcontroller applications that render untrusted styled text
Qt-based firmware consuming external HTML-like content for UI rendering

Discovery Timeline

2026-10-05 - CVE-2026-19395 published to NVD
2026-10-06 - Last updated in NVD database

Technical Details for CVE-2026-19395

Vulnerability Analysis

The vulnerability resides in the styled text parser used by the Qt for MCUs Text element. When the parser encounters an <img> tag, it extracts attribute values and passes them to an internal validation routine. That routine rejects empty strings and reports an error. Because the default error handler on Qt for MCUs halts the device, a single malformed tag converts a rendering error into a full availability failure. The flaw maps to [CWE-230: Improper Handling of Missing Values].

The impact is limited to availability. The CVE record indicates no confidentiality or integrity consequences, consistent with a parser-induced halt rather than memory corruption or data exposure.

Root Cause

The parser does not sanitize or default empty attribute values before forwarding them to the internal check. The downstream check treats empty input as an error condition rather than an acceptable or ignorable state. The chosen error handler escalates a parser-level issue to a device-level halt, violating fail-safe expectations for embedded UI rendering.

Attack Vector

An attacker supplies styled text containing an <img> tag with any attribute whose value is empty, for example src="" or alt="". Any input channel that feeds a Text element configured for styled text can serve as the delivery path. On devices that render content received over a network interface, exploitation requires no authentication and no user interaction. The result is a device halt that interrupts the embedded application until the hardware is reset.

No verified public proof-of-concept code is available at publication. Technical details are tracked on the Qt Known Vulnerabilities List.

Detection Methods for CVE-2026-19395

Indicators of Compromise

Unexpected device halts or watchdog resets correlated with UI updates or incoming styled text
Log entries from Qt for MCUs error handlers referencing empty attribute values in the text parser
Repeated reboot cycles following external content ingestion from network, serial, or file inputs

Detection Strategies

Inspect application logs and crash telemetry for parser errors tied to <img> tag processing
Perform static review of firmware code paths that assign untrusted strings to styled Text elements
Run fuzz tests against the styled text pipeline using malformed HTML-like tags with empty attributes

Monitoring Recommendations

Monitor device uptime and reset counters on fleets running Qt for MCUs applications
Capture serial or diagnostic output during QA for parser errors referencing attribute validation
Centralize embedded device health telemetry in a SIEM to correlate halts across the fleet

How to Mitigate CVE-2026-19395

Immediate Actions Required

Identify firmware images using Qt for MCUs with styled text rendering of externally sourced content
Restrict or sanitize untrusted input before it reaches any Text element configured for styled text
Replace the default error handler with a non-halting handler where application safety allows

Patch Information

Refer to the Qt Known Vulnerabilities List for the fixed version and vendor remediation guidance. Rebuild and reflash affected devices using a patched Qt for MCUs release once available.

Workarounds

Strip or reject <img> tags from untrusted styled text before rendering
Pre-validate attribute values and remove any attribute whose value is empty
Switch affected Text elements to plain text rendering when styled formatting is not required
Install a custom error handler that logs parser errors without halting the device

bash

# Example input filter applied before assigning text to a styled Text element
# Removes <img> tags that contain empty attribute values (attr="")
sanitized=$(printf '%s' "$input" | sed -E 's/<img[^>]*[a-zA-Z-]+=""[^>]*>//g')