Out-of-bounds read in QTextCodec::codecForName() in Qt

Summary

CVE	CVE-2026-9499
State	PUBLISHED
Assigner	TQtC
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-07-21 14:16:35 UTC
Updated	2026-07-22 19:17:14 UTC
Description	An out-of-bounds read (buffer over-read) vulnerability exists in QTextCodec::codecForName() in Qt. When the function is called with a QByteArray that is not NUL-terminated (for example, one created with QByteArray::fromRawData()), the codec-name matching routine reads past the end of the supplied buffer. In most cases this results in an incorrect text codec being selected; in the worst case, if the over-read reaches unmapped memory, the process crashes (denial of service). The over-read is bounded by the length of the longest codec-name candidate, and the out-of-bounds bytes are only compared internally against Qt's fixed list of codec names, so no data is disclosed to an attacker. Applications that do not pass non-NUL-terminated QByteArrays to QTextCodec::codecForName() are not exposed. The affected code resides in the Qt5Compat module from Qt 6.0.0 onward, and in Qt Core (qtbase) in Qt 4.x and Qt 5.x.

Risk And Classification

Primary CVSS: v4.0 6.3 MEDIUM from a59d8014-47c4-4630-ab43-e1b13cbe58e3

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/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

EPSS: 0.003010000 probability, percentile 0.222820000 (date 2026-07-22)

Problem Types: CWE-125 | CWE-125 CWE-125 Out-of-bounds Read

Version	Source	Type	Score	Severity	Vector
4.0	a59d8014-47c4-4630-ab43-e1b13cbe58e3	Secondary	6.3	MEDIUM	`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/C...`
4.0	CNA	CVSS	6.3	MEDIUM	`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N`

CVSS v4.0 Breakdown

Attack Vector

Network

Attack Complexity

Low

Attack Requirements

Present

Privileges Required

None

User Interaction

None

Confidentiality

None

Integrity

Low

Availability

Low

Sub Conf.

None

Sub Integrity

None

Sub Availability

None

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/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

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Qt	Qt	affected 6.0.0 6.8.8 python	Not specified
CNA	Qt	Qt	affected 6.9.0 6.11.1 python	Not specified
CNA	Qt	Qt	affected 4.0.0 6.0.0 python	Not specified

References

Reference	Source	Link	Tags
codereview.qt-project.org/c/qt/tqtc-qt5compat/+/725112	a59d8014-47c4-4630-ab43-e1b13cbe58e3	codereview.qt-project.org
codereview.qt-project.org/c/qt/qt5compat/+/724995	a59d8014-47c4-4630-ab43-e1b13cbe58e3	codereview.qt-project.org
codereview.qt-project.org/c/qt/qt5compat/+/723911	a59d8014-47c4-4630-ab43-e1b13cbe58e3	codereview.qt-project.org
codereview.qt-project.org/c/qt/qt5compat/+/724348	a59d8014-47c4-4630-ab43-e1b13cbe58e3	codereview.qt-project.org
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

Additional Advisory Data

Solutions

CNA: Update to Qt 6.8.8, Qt 6.11.1, Qt 6.12.0, or later, or apply the referenced patch.

There are currently no legacy QID mappings associated with this CVE.