# CVE-2026-101201: Qt binary JSON out-of-bounds read in QBinaryJson::fromBinaryData

Source: https://junglewise.ai/threats/cve-2026-101201-a-malformed-header-in-the-binary-file-fed-to-qbinaryjson  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-20. Updated: 2026-10-20  
License: CC BY 4.0 with a link back

CVE-2026-101201 · Severity: info · Published 2026-10-20

Qt is a widely used framework for building cross-platform desktop and mobile applications. A malformed binary JSON file can trigger an out-of-bounds read in Qt's JSON parsing, potentially causing the application to crash or exhibit undefined behavior. This could be exploited by an attacker distributing malicious JSON files to crash applications that parse untrusted input.

Vendors: [Qt](https://junglewise.ai/threats/vendors/qt).

## Quick answers

**Is CVE-2026-101201 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-101201 being exploited in the wild.

**How severe is CVE-2026-101201?** Informational severity, published 20 October 2026.

**Which products and versions are affected?** Qt qt5compat.

**Is there a fix for CVE-2026-101201?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-101201 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-101201?** Check whether you run Qt5compat. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

QBinaryJson::fromBinaryData fails to properly validate the header of a binary JSON file before reading beyond allocated buffer bounds. The vulnerability is triggered by parsing a malformed header and results in an out-of-bounds read. This is a memory safety issue affecting the Qt5compat module and requires the application to parse user-supplied or untrusted binary JSON input.

## Affected products

- Qt qt5compat

## Timeline

- 2026-10-20: disclosed

## References

- [https://codereview.qt-project.org/c/qt/qt5compat/+/758925](https://codereview.qt-project.org/c/qt/qt5compat/+/758925)
- [https://codereview.qt-project.org/c/qt/qt5compat/+/759230](https://codereview.qt-project.org/c/qt/qt5compat/+/759230)

## Related threats

- [Qt integer overflow in XML parsing](https://junglewise.ai/threats/cve-2026-100140-an-integer-overflow-vulnerability-in-the-qt-xml-parsing)