CVE-2018-21035Network attack vector

Remote memory exhaustion via oversized WebSocket payloads

Published Feb 28, 2020 · Updated Aug 5, 2024

Denial of service in Qt WebSockets 5.14.1 and earlier allows remote attackers to exhaust memory via oversized incoming frames or messages. The QWebSocket receive path accepts frames and reassembled messages as large as 2 GB because no public API sets lower limits. Sending such payloads to a network-reachable application using the module consumes excessive virtual memory and interrupts that application.

CVSS severity7.5
High
EPSS probability2.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Qt WebSockets 5.14.1 and earlier allows remote attackers to exhaust memory via oversized incoming frames or messages. The QWebSocket receive path accepts frames and reassembled messages as large as 2 GB because no public API sets lower limits. Sending such payloads to a network-reachable application using the module consumes excessive virtual memory and interrupts that application.

The record

CVE
CVE-2018-21035
Published
Feb 28, 2020
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-770, T1499.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 28, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
8.6MITRECVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.002Service Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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