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No exploitation reportedFix available

CVE-2018-21035

No exploitation reported by the sources we read.

  • Published2020-02-28
  • WeaknessCWE-770

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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).

Timeline

dates in UTC
  1. 2020-02-2821:15CVE publishedNVD

Versions per branch

NVD
Qt
BranchAffectedFixed in
5.14≤ 5.14.1no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • qt5-qtbaseRed Hat:enterprise_linux:8::appstreamall versions · fixed in 0:5.12.5-6.el8and 17 other packages
  • qt5-qtbase-staticRed Hat:enterprise_linux:8::crball versions · fixed in 0:5.12.5-6.el8and 9 other packages
  • qt5-qtbase-staticAlmaLinux:8all versions · fixed in 5.12.5-6.el8
  • qt5-qtsvgAzure Linux:2all versions · fixed in 5.12.11-3
  • qt5-qttoolsRed Hat:enterprise_linux:8::appstreamall versions · fixed in 0:5.12.5-2.el8and 32 other packages
  • qt5-qttools-staticRed Hat:enterprise_linux:8::crball versions · fixed in 0:5.12.5-2.el8and 13 other packages
  • qt5-qttools-staticAlmaLinux:8all versions · fixed in 5.12.5-2.el8
  • qt5-qtwebsocketsRocky Linux:8all versions · fixed in 0:5.12.5-2.el8

7 more package ranges on OSV.dev

Vendor advisories

  • CVE-2018-21035 Red Hat Product Security363 products fixed · 5 known affected

    qt5-qtwebsockets: websocket implementation allows only limited size for frames and messages therefore attacker can cause DOS

    qt5-qtwebsockets as a component of Red Hat Enterprise Linux 7 · qt5-qtwebsockets-devel as a component of Red Hat Enterprise Linux 7 · qt5-qtwebsockets-doc as a component of Red Hat Enterprise Linux 7 · +2 more

  • RHSA-2020:4690 Red Hat Product Security363 products fixed

    Red Hat Security Advisory: qt5-qtbase and qt5-qtwebsockets security and bug fix update

Full record on NVD

Fix

  1. Vendor fix Red Hat Product Security RHSA-2020:4690 · 363 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  2. No fix planned, says the vendor Red Hat Product Security CVE-2018-21035 · 5 productsWill not fix

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • NVDCVSS 3.17.5read 2026-10-23
  • CNACVSS 3.08.6known since 2026-10-23
  • NVDCVSS 2.05read 2026-10-23
  • NVDweakness (CWE)CWE-770read 2026-10-23
  • FIRST EPSSEPSS score2.3 %2026-11-08
  • OSVaffected packages—
  • GitHub Advisoriesadvisory—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2020-02-28
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-xhq4-5269-2ffv

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).

Is CVE-2018-21035 actively exploited?

Active exploitation of CVE-2018-21035 has not been confirmed. Its EPSS score was 2.3% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2018-21035?

CVE-2018-21035 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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