How severe is CVE-2018-21035?

CVE-2018-21035 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2018-21035 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-21035?

CVE-2018-21035 affects Qt. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2018-21035?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2018-21035 published?

CVE-2018-21035 was published on 2020-02-28 and last updated on 2026-06-17.

CVE-2018-21035

CVE-2018-21035 is a high-severity vulnerability in Qt with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-770.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 2% (83rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-770
Affected product: Qt
Published: 2020-02-28
Last modified: 2026-06-17

Description

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).

Frequently asked questions

What is 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).
How severe is CVE-2018-21035?: CVE-2018-21035 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2018-21035 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (83rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2018-21035?: CVE-2018-21035 affects Qt. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2018-21035?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2018-21035 published?: CVE-2018-21035 was published on 2020-02-28 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:qt:qt:*:*:*:*:*:*:*:*

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