Security readout for executives and security teams
Plain-English summary
Windows applications using affected Qt versions as Schannel-backed TLS servers may gradually lose resources when handling many incoming connections. Over time, this incomplete cleanup can make the service unavailable. The issue threatens availability rather than documented data confidentiality or integrity.
Executive priority
Prioritize internet-facing or business-critical Windows TLS services using affected Qt versions. Schedule prompt remediation because unauthenticated network traffic can threaten service availability, while recognizing that the supplied evidence does not show active exploitation.
Technical view
CVE-2025-6338 is a CWE-459 incomplete-cleanup flaw in Qt Network's Windows Schannel support. Affected server-side TLS connection handling can cause prolonged resource exhaustion and denial of service. CVSS 4.0 scores it 9.2: remotely reachable, low complexity, unauthenticated, and requiring no user interaction.
Likely exposure
Exposure is most likely in Windows services built with Qt 5.15.0–6.8.3 or Qt 6.9.0–6.9.1 that accept incoming TLS connections through Schannel. The bundle does not establish exposure for clients, non-Windows systems, or alternative TLS backends.
Exploitation context
The CVSS vector indicates remote, low-complexity, unauthenticated reachability. However, the source bundle reports no KEV listing and provides no evidence of active exploitation or public weaponization. Service disruption reportedly develops over a long period rather than necessarily occurring immediately.
Researcher notes
The record identifies incomplete cleanup but does not quantify connection volume, exhaustion timing, affected resource type, or practical impact by deployment. Researchers should inspect the referenced Qt change and reproduce only in controlled environments. No confidentiality or integrity impact is documented.
Mitigation direction
- Inventory Windows services using Qt Network, Schannel, and server-side TLS.
- Upgrade affected 5.x or 6.8.x deployments to Qt 6.8.4 or another vendor-supported unaffected release.
- Upgrade Qt 6.9.0 or 6.9.1 deployments to 6.9.2 or later.
- Check Qt guidance and the referenced code review before deploying changes.
- Apply connection controls and resource monitoring where immediate upgrades are unavailable.
Validation and detection
- Confirm each service's operating system, Qt version, TLS role, and backend.
- Verify upgraded builds no longer fall within the documented affected ranges.
- Review connection and resource telemetry for sustained growth under normal incoming TLS traffic.
- Run authorized availability regression testing without targeting production services.
- Confirm service stability after remediation during prolonged, representative connection loads.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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.
CWE-459: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2025-6338 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.2 (4.0)
- Known Exploited
- No
- Published
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
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.
SSVC decision data
CVSS vector scores
1 official scoreWe 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.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H——TQtCVulnerability scoring details
Base CVSS 4.0 score
9.2CriticalVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://codereview.qt-project.org/c/qt/qtbase/+/651495CVE reference, TQtC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Incomplete Cleanup
Incomplete Cleanup represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.