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CVE-2026-16762: Denial-of-service vulnerability in the Qt Core QXmlStream parser (QXmlStreamReader) impacts Qt

• Severity: high (CVSS 8.7 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-23 · updated 2026-10-23
• Weakness: CWE-407

Description

An attacker able to supply a crafted XML document to an application using QXmlStreamReader can cause disproportionate CPU consumption during parsing, making the application unresponsive (denial of service). Exploitation requires only that the application parse attacker-influenced XML; no authentication, privileges, or user interaction beyond ingesting the input are needed. There is no loss of confidentiality or integrity — no data disclosure, data modification, or code execution — and the impact is contained to the affected process.

Affected products

• Qt: from 4.3.0 before 6.8.9; from 6.9.0 before 6.11.2 — fixed in 6.11.2, 6.8.9

How to fix

Upgrade to a fixed version: Qt 6.11.2, 6.8.9. Check the vendor advisory for mitigations.

References

• https://codereview.qt-project.org/c/qt/qtbase/+/738885
• https://codereview.qt-project.org/c/qt/qtbase/+/738901
• https://wiki.qt.io/List_of_known_vulnerabilities_in_Qt_products#CVE-2026-16762:

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