What is CVE-2018-21035?

CVE-2018-21035 is a high-severity vulnerability in Qt, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 7.5/10. Published 2020-02-28.

How severe is CVE-2018-21035?

High severity. CVSS v3 base score is 7.5 out of 10.

Is CVE-2018-21035 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Resource exhaustion in Qt

CVE-2018-21035

In Qt through 5.14.1, the WebSocket implementation accepts up to 2GB for frames and 2GB for messages. Smaller limits cannot be configured. This makes it easier for attackers to cause a denial of service (memory consumption).

Published 2020-02-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.023 (82.9th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 83rd percentile — 82.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.023 · newest: 0.023 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-770 — Allocation of Resources Without Limits or Throttling

Public proof-of-concept exploits

PalindromeLabs/awesome-websocket-security

References

codereview.qt-project.org/c/qt/qtwebsockets/+/284735 (Patch, Third Party Advisory)
bugreports.qt.io/browse/QTBUG-70693 (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2018-21035?: CVE-2018-21035 is a high-severity vulnerability in Qt, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 7.5/10. Published 2020-02-28.
How severe is CVE-2018-21035?: High severity. CVSS v3 base score is 7.5 out of 10.
Is CVE-2018-21035 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.