CVE-2025-6338 | Possible denial of service with multiple incoming connections to a Schannel based server with a TLS backend

There is an incomplete cleanup vulnerability in Qt Network's Schannel support on Windows which can lead to a Denial of Service over a long period.This issue affects Qt from 5.15.0 through 6.8.3, from 6.9.0 before 6.9.2.

Published: 2025-10-16 Last update: 2026-04-15 Assigner: a59d8014-47c4-4630-ab43-e1b13cbe58e3 Source: a59d8014-47c4-4630-ab43-e1b13cbe58e3
NVD Status：Deferred，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-6338 is rated Moderate Risk (46/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.09%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-6338

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-02-15 0.04% 0.09% +0.05%
2 2025-11-27 0.06% 0.04% -0.01%
3 2025-10-22 — 0.06% —

Full EPSS history (4 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-6338

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.2 4.0 CRITICAL
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:L)
Exploitation conditions are straightforward and stable.
Attack requirements (AT:N)
No additional preconditions are required beyond normal reachability.
Privileges required (PR:N)
No privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:N)
No confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:N)
No integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:H)
High availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:H)
High availability impact on subsequent systems.
Exploit maturity (threat) (E:X)
Not defined: no reliable threat intelligence; scoring assumes the worst case (equivalent to Attacked).
Confidentiality requirement (CR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Integrity requirement (IR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Availability requirement (AR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Modified attack vector (MAV:X)
Not defined: scoring uses the Base Attack Vector (AV).
Modified attack complexity (MAC:X)
Not defined: scoring uses the Base Attack Complexity (AC).
Modified attack requirements (MAT:X)
Not defined: scoring uses the Base Attack Requirements (AT).
Modified privileges required (MPR:X)
Not defined: scoring uses the Base Privileges Required (PR).
Modified user interaction (MUI:X)
Not defined: scoring uses the Base User Interaction (UI).
Modified vulnerable system confidentiality impact (MVC:X)
Not defined: scoring uses the Base VC metric.
Modified vulnerable system integrity impact (MVI:X)
Not defined: scoring uses the Base VI metric.
Modified vulnerable system availability impact (MVA:X)
Not defined: scoring uses the Base VA metric.
Modified subsequent system confidentiality impact (MSC:X)
Not defined: scoring uses the Base SC metric.
Modified subsequent system integrity impact (MSI:X)
Not defined: scoring uses the Base SI metric.
Modified subsequent system availability impact (MSA:X)
Not defined: scoring uses the Base SA metric.
Safety (supplemental) (S:X)
Not evaluated.
Automatable (supplemental) (AU:X)
Not evaluated.
Recovery (supplemental) (R:X)
Not evaluated.
Value density (supplemental) (V:X)
Not evaluated.
Vulnerability response effort (supplemental) (RE:X)
Not evaluated.
Provider urgency (supplemental) (U:X)
Not evaluated.
 — — a59d8014-47c4-4630-ab43-e1b13cbe58e3

Weakness enumeration for CVE-2025-6338

OS Trackers for CVE-2025-6338

vendor priority summary link
debian unimportant CVE-2025-6338 unimportant priority: Debian including 1 source packages (qt6-base), 4 status rows across 4 suites (bookworm, forky, sid, trixie): resolved 4. https://security-tracker.debian.org/tracker/CVE-2025-6338
ubuntu medium CVE-2025-6338 medium priority: Ubuntu including 1 source packages (qt6-base), 5 status rows across 5 suites (jammy, noble, plucky, questing, upstream): not-affected 5. https://ubuntu.com/security/CVE-2025-6338

Affected software / configurations for CVE-2025-6338

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2025-6338

cvelogic Threat Intelligence