LiveActive security incident?Get immediate response
CVE Record

CVE-2018-21035: In Qt through 5.14.1, the WebSocket implementation accepts up to 2GB for frames and 2GB for messages.

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).

HighCVSS 8.6Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

Qt applications using the affected WebSocket implementation may allow a remote party to force excessive memory use. The issue is denial of service, not data theft or code execution based on the supplied sources.

Executive priority

Treat as high priority for internet-facing or business-critical Qt WebSocket services because exploitation could interrupt availability. Internal-only or non-WebSocket Qt applications are lower urgency after inventory confirms scope.

Technical view

Qt WebSockets through 5.14.1 accepts WebSocket frames up to 2GB and messages up to 2GB, with no smaller configurable limits. An unauthenticated network attacker could cause high memory consumption and service disruption.

Likely exposure

Exposure is most likely in applications or services built with Qt WebSockets through 5.14.1 that accept untrusted WebSocket connections. The source bundle does not provide CPEs or a complete affected-product list.

Exploitation context

The bundle does not show CISA KEV listing or cited evidence of active exploitation. The documented attack impact is availability loss through memory consumption, with network reachability and no privileges required per CVSS.

Researcher notes

The supplied data has limited affected-product metadata and no CWE entry. Analysis should focus on Qt WebSockets versioning, exposure of WebSocket endpoints, and whether the referenced Qt change is present in the deployed build.

Mitigation direction

  • Inventory applications using Qt WebSockets and record Qt versions.
  • Check Qt guidance, bug QTBUG-70693, and code review 284735 for the supported fix path.
  • Upgrade affected Qt WebSockets deployments when vendor-supported fixed releases are available.
  • Reduce exposure of untrusted WebSocket endpoints where business operations allow.
  • Use perimeter controls that enforce conservative WebSocket size and rate limits where applicable.

Validation and detection

  • Confirm whether deployed Qt versions are through 5.14.1.
  • Identify public or partner-facing WebSocket endpoints backed by Qt WebSockets.
  • Review application code for QWebSocket or QWebSocketServer usage.
  • Verify current controls reject excessive WebSocket sizes without testing production destructively.
  • Monitor affected services for memory exhaustion and abnormal WebSocket traffic patterns.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2018-21035 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
8.6 (3.0)
Known Exploited
No
Published

Vector: CVSS:3.0/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:C/UI:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.6CVSS 3.0HighCVSS:3.0/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:C/UI:N3.94Primary CVE score

Vulnerability scoring details

Base CVSS 3.0 score

8.6High
CVSS 3.0 vector shape for CVE-2018-21035Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.0/AC:L/AV:N/A:H/C:N/I:N/PR:N/S:C/UI:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.