CVE-2026-9499 Out-of-bounds read in QTextCodec::codecForName() in Qt
An out-of-bounds read in Qt's QTextCodec can cause a denial of service when processing non-NUL-terminated byte arrays.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-9499?
CVE-2026-9499 is a medium-severity memory corruption vulnerability in Qt, published on 21 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-125
Which versions are affected by CVE-2026-9499?
Linux distribution packages (40)
qt6-qt5compat AlmaLinux:10 | All versions | 6.10.1-1.el10_2.1 |
qt6-qt5compat-devel AlmaLinux:10 | All versions | 6.10.1-1.el10_2.1 |
qt6-qt5compat-examples AlmaLinux:10 | All versions | 6.10.1-1.el10_2.1 |
qt5-qtbase AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-common AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-devel AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-examples AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-gui AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-mysql AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-odbc AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-postgresql AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-private-devel AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase-static AlmaLinux:8 | All versions | 5.15.3-9.el8_10 |
qt5-qtbase AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-common AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-devel AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-examples AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-gui AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-mysql AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-odbc AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-postgresql AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-private-devel AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt5-qtbase-static AlmaLinux:9 | All versions | 5.15.9-11.el9_8.1 |
qt6-qt5compat Red Hat:enterprise_linux:10.2 | All versions | 0:6.10.1-1.el10_2.1 |
qt6-qt5compat-debuginfo Red Hat:enterprise_linux:10.2 | All versions | 0:6.10.1-1.el10_2.1 |
qt6-qt5compat-debugsource Red Hat:enterprise_linux:10.2 | All versions | 0:6.10.1-1.el10_2.1 |
qt6-qt5compat-devel Red Hat:enterprise_linux:10.2 | All versions | 0:6.10.1-1.el10_2.1 |
qt6-qt5compat-examples Red Hat:enterprise_linux:10.2 | All versions | 0:6.10.1-1.el10_2.1 |
qt6-qt5compat-examples-debuginfo Red Hat:enterprise_linux:10.2 | All versions | 0:6.10.1-1.el10_2.1 |
qt6-qt5compat-tests-debuginfo Red Hat:enterprise_linux:10.2 | All versions | 0:6.10.1-1.el10_2.1 |
qt5-qtbase Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-common Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-debugsource Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-devel Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-devel-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-examples Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-examples-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-gui Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
qt5-qtbase-gui-debuginfo Red Hat:enterprise_linux:8::appstream | All versions | 0:5.15.3-9.el8_10 |
How do I fix CVE-2026-9499?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-9499 being exploited?
There is no known exploitation of CVE-2026-9499 in the wild and no public exploit code.
Sources
Also known as ALSA-2026:65816, ALSA-2026:65897, ALSA-2026:65993, CLSA-2026-1789398784, DEBIAN-CVE-2026-9499, ECHO-5c6a-872b-49bb and 25 more.