CVE-2025-5991 | Use after free in QHttp2ProtocolHandler

There is a "Use After Free" vulnerability in Qt's QHttp2ProtocolHandler in the QtNetwork module. This only affects HTTP/2 handling, HTTP handling is not affected by this at all. This happens due to a race condition between how QHttp2Stream uploads the body of a POST request and the simultaneous handling of HTTP error responses. This issue only affects Qt 6.9.0 and has been fixed for Qt 6.9.1.

Published: 2025-06-11 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-2025-5991 is rated Low Risk (17/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.08%). Low composite risk—no urgent action required; patch on your normal maintenance cycle and revisit priority if CVSS or EPSS increases.

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-2025-5991

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 2026-04-07 0.01% 0.08% +0.07%
2 2025-06-11 — 0.01% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-5991

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
2.1 4.0 LOW
CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:L/SI:L/SA:L/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:L)
Attacker needs local access on the target system.
Attack complexity (AC:H)
Exploitation depends on constrained or hard-to-reproduce conditions.
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:L)
Limited confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:L)
Limited integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:L)
Limited availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:L)
Limited confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:L)
Limited integrity impact on subsequent systems.
Subsequent system availability impact (SA:L)
Limited 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-2025-5991

OS Trackers for CVE-2025-5991

vendor priority summary link
debian unimportant CVE-2025-5991 unimportant priority: Debian including 3 source packages (qt6-base, qtbase-opensource-src, qtbase-opensource-src-gles), 14 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 14. https://security-tracker.debian.org/tracker/CVE-2025-5991
redhat medium — https://access.redhat.com/security/cve/CVE-2025-5991
suse medium CVE-2025-5991 severity moderate: SUSE including 146 source package names (libQt5Bootstrap-devel-static, libQt5Bootstrap-devel-static-32bit, …), 1394 product×package rows across 35 product lines (SLES-LTSS-TERADATA 15 SP2, SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS, … (35 product lines)): Known Not Affected 1394. https://www.suse.com/security/cve/CVE-2025-5991/
ubuntu medium CVE-2025-5991 medium priority: Ubuntu including 3 source packages (qt6-base, qtbase-opensource-src, qtbase-opensource-src-gles), 23 status rows across 9 suites (bionic, focal, jammy, noble, oracular, plucky, questing, upstream, xenial): needs-triage 10, not-affected 7, ignored 5, released 1. https://ubuntu.com/security/CVE-2025-5991

Affected software / configurations for CVE-2025-5991

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2025-5991

cvelogic Threat Intelligence