🛡️ CVE-2023-4921 on Ubuntu — linux

⚪ Unknown ✅ No Known Exploit OSV

N/A

CVSS Score

0 Low4 Medium7 High9 Critical10

Description

A use-after-free vulnerability in the Linux kernel's net/sched: sch_qfq component can be exploited to achieve local privilege escalation. When the plug qdisc is used as a class of the qfq qdisc, sending network packets triggers use-after-free in qfq_dequeue() due to the incorrect .peek handler of sch_plug and lack of error checking in agg_dequeue(). We recommend upgrading past commit 8fc134fee27f2263988ae38920bc03da416b03d8.

Distribution advisory

This page covers CVE-2023-4921 as tracked by Ubuntu, for the package linux. The fix is available in version 5.15.0-87.97; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity high, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Attack vector: Local — a local account, shell or session on the host is needed.
Attack complexity: Low — the attack works reliably, with no preparation.
Privileges required: Low — an ordinary user account is enough.
User interaction: None — nobody has to be tricked into anything.
Scope: Unchanged — the damage stays inside the vulnerable component.
Confidentiality impact: High — total loss, or loss the attacker controls.
Integrity impact: High — total loss, or loss the attacker controls.
Availability impact: High — total loss, or loss the attacker controls.

Weakness class

UBUNTU-CVE-2023-4921 is classified as CWE-416: Use After Free. Memory is used after being released, so its contents may already belong to something else.

Affected software

UBUNTU-CVE-2023-4921 is recorded against 111 packages.

linux (fixed in 5.15.0-87.97)
linux-allwinner-5.19
linux-aws (fixed in 5.15.0-1048.53)
linux-aws-5.0
linux-aws-5.11
linux-aws-5.13
linux-aws-5.15 (fixed in 5.15.0-1048.53~20.04.1)
linux-aws-5.19
linux-aws-5.3
linux-aws-5.4 (fixed in 5.4.0-1112.121~18.04.2)
linux-aws-5.8
linux-aws-6.2 (fixed in 6.2.0-1014.14~22.04.1)
linux-aws-6.5
linux-aws-fips
linux-aws-hwe (fixed in 4.15.0-1162.175~16.04.1)
linux-azure (fixed in 5.15.0-1050.57)
linux-azure-4.15 (fixed in 4.15.0-1171.186)
linux-azure-5.11
linux-azure-5.13
linux-azure-5.15 (fixed in 5.15.0-1050.57~20.04.1)
linux-azure-5.19
linux-azure-5.3
linux-azure-5.4 (fixed in 5.4.0-1118.125~18.04.1)
linux-azure-5.8

Show the remaining 87 packages

linux-azure-6.2 (fixed in 6.2.0-1015.15~22.04.1)
linux-azure-6.5
linux-azure-edge
linux-azure-fde
linux-azure-fde-5.19
linux-azure-fde-6.2 (fixed in 6.2.0-1015.15~22.04.1.1)
linux-azure-fde-6.8
linux-azure-fips
linux-bluefield
linux-fips
linux-gcp (fixed in 5.15.0-1045.53)
linux-gcp-4.15 (fixed in 4.15.0-1156.173)
linux-gcp-5.11
linux-gcp-5.13
linux-gcp-5.15 (fixed in 5.15.0-1045.53~20.04.2)
linux-gcp-5.19
linux-gcp-5.3
linux-gcp-5.4 (fixed in 5.4.0-1116.125~18.04.1)
linux-gcp-5.8
linux-gcp-6.2 (fixed in 6.2.0-1017.19~22.04.1)
linux-gcp-fips
linux-gke (fixed in 5.15.0-1045.50)
linux-gke-4.15
linux-gke-5.15
linux-gke-5.4
linux-gkeop (fixed in 5.15.0-1031.37)
linux-gkeop-5.15 (fixed in 5.15.0-1031.37~20.04.1)
linux-gkeop-5.4
linux-hwe
linux-hwe-5.11
linux-hwe-5.13
linux-hwe-5.15 (fixed in 5.15.0-87.97~20.04.1)
linux-hwe-5.19
linux-hwe-5.4 (fixed in 5.4.0-165.182~18.04.1)
linux-hwe-5.8
linux-hwe-6.2 (fixed in 6.2.0-35.35~22.04.1)
linux-hwe-edge
linux-ibm (fixed in 5.15.0-1041.44)
linux-ibm-5.15 (fixed in 5.15.0-1041.44~20.04.1)
linux-ibm-5.4 (fixed in 5.4.0-1059.64~18.04.1)
linux-intel-5.13
linux-intel-iot-realtime (fixed in 5.15.0-1041.43)
linux-intel-iotg (fixed in 5.15.0-1043.49)
linux-intel-iotg-5.15 (fixed in 5.15.0-1043.49~20.04.1)
linux-iot (fixed in 5.4.0-1024.25)
linux-kvm (fixed in 5.15.0-1045.50)
linux-lowlatency (fixed in 5.15.0-87.96)
linux-lowlatency-hwe-5.15 (fixed in 5.15.0-87.96~20.04.1)
linux-lowlatency-hwe-5.19
linux-lowlatency-hwe-6.2 (fixed in 6.2.0-1015.15~22.04.1)
linux-lts-xenial (fixed in 4.4.0-246.280~14.04.1)
linux-nvidia (fixed in 5.15.0-1039.39)
linux-nvidia-6.2 (fixed in 6.2.0-1011.11)
linux-nvidia-6.5 (fixed in 6.5.0-1007.7)
linux-nvidia-tegra (fixed in 5.15.0-1019.19)
linux-nvidia-tegra-5.15 (fixed in 5.15.0-1019.19~20.04.1)
linux-nvidia-tegra-igx (fixed in 5.15.0-1006.6)
linux-oem
linux-oem-5.10
linux-oem-5.13
linux-oem-5.14
linux-oem-5.17
linux-oem-5.6
linux-oem-6.0
linux-oem-6.1 (fixed in 6.1.0-1025.25)
linux-oem-6.5 (fixed in 6.5.0-1007.7)
linux-oracle (fixed in 5.15.0-1046.52)
linux-oracle-5.0
linux-oracle-5.11
linux-oracle-5.13
linux-oracle-5.15 (fixed in 5.15.0-1046.52~20.04.1)
linux-oracle-5.3
linux-oracle-5.4 (fixed in 5.4.0-1111.120~18.04.1)
linux-oracle-5.8
linux-raspi (fixed in 5.15.0-1041.44)
linux-raspi-5.4 (fixed in 5.4.0-1096.107~18.04.1)
linux-raspi-realtime
linux-raspi2
linux-realtime (fixed in 5.15.0-1049.55)
linux-riscv
linux-riscv-5.11
linux-riscv-5.15 (fixed in 5.15.0-1044.48~20.04.1)
linux-riscv-5.19
linux-riscv-5.8
linux-starfive-5.19
linux-starfive-6.2 (fixed in 6.2.0-1007.8~22.04.1)
linux-xilinx-zynqmp (fixed in 5.15.0-1025.29)

Timeline and source

Published on 12 September 2023 and last revised on 17 August 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

Other advisories for this package

linux has other advisories on record. If you are patching this one, these are worth checking on the same host:

DEBIAN-CVE-2022-4994 (published 30 Jul 2026)
CVE-2026-35233 (4.4 Medium, published 1 May 2026)
CVE-2026-21996 (3.3 Low, published 1 May 2026)
CVE-2026-21991 (5.5 Medium, published 16 Mar 2026)
CGA-mcwh-q4vm-9f29 (published 29 Jan 2026)
CGA-w6xv-3fg4-grm5 (published 29 Jan 2026)
CGA-4fpx-x3w2-4hfv (published 7 Jan 2026)
CGA-fv2v-4h6c-q367 (published 7 Jan 2026)

Same weakness in other software

These advisories are the same class of weakness (CWE-416: Use After Free) in other software:

CVE-2022-21540 (5.3 Medium, published 8 May 2026)
CVE-2022-50552 (7.8 High, published 7 Oct 2025)
CVE-2022-50542 (7.8 High, published 7 Oct 2025)
CVE-2022-50507 (7.8 High, published 4 Oct 2025)
CVE-2022-50496 (7.8 High, published 4 Oct 2025)
CVE-2022-50492 (7.8 High, published 4 Oct 2025)
CVE-2022-50488 (7.8 High, published 4 Oct 2025)
CVE-2022-50454 (7.8 High, published 1 Oct 2025)

CVE-2023-4921 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

BellSoft — BELL-CVE-2023-4921 Base record — CVE-2023-4921 Debian — DEBIAN-CVE-2023-4921

Details

Severity Unknown

CVSS Score N/A

CVSS Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CWE N/A

Public Exploit ✅ No

Source OSV

Published 2023-09-12

Updated 2026-08-20

Modified 2026-08-17

Fix URL N/A

Affected Packages

Software	From version	Fixed in
linux	—	5.15.0-87.97
linux-allwinner-5.19	—	—
linux-aws	—	5.15.0-1048.53
linux-aws-5.0	—	—
linux-aws-5.11	—	—
linux-aws-5.13	—	—
linux-aws-5.15	—	5.15.0-1048.53~20.04.1
linux-aws-5.19	—	—
linux-aws-5.3	—	—
linux-aws-5.4	—	5.4.0-1112.121~18.04.2
linux-aws-5.8	—	—
linux-aws-6.2	—	6.2.0-1014.14~22.04.1
linux-aws-6.5	—	—
linux-aws-fips	—	—
linux-aws-hwe	—	4.15.0-1162.175~16.04.1
linux-azure	—	5.15.0-1050.57
linux-azure-4.15	—	4.15.0-1171.186
linux-azure-5.11	—	—
linux-azure-5.13	—	—
linux-azure-5.15	—	5.15.0-1050.57~20.04.1
linux-azure-5.19	—	—
linux-azure-5.3	—	—
linux-azure-5.4	—	5.4.0-1118.125~18.04.1
linux-azure-5.8	—	—
linux-azure-6.2	—	6.2.0-1015.15~22.04.1
linux-azure-6.5	—	—
linux-azure-edge	—	—
linux-azure-fde	—	—
linux-azure-fde-5.19	—	—
linux-azure-fde-6.2	—	6.2.0-1015.15~22.04.1.1
linux-azure-fde-6.8	—	—
linux-azure-fips	—	—
linux-bluefield	—	—
linux-fips	—	—
linux-gcp	—	5.15.0-1045.53
linux-gcp-4.15	—	4.15.0-1156.173
linux-gcp-5.11	—	—
linux-gcp-5.13	—	—
linux-gcp-5.15	—	5.15.0-1045.53~20.04.2
linux-gcp-5.19	—	—
linux-gcp-5.3	—	—
linux-gcp-5.4	—	5.4.0-1116.125~18.04.1
linux-gcp-5.8	—	—
linux-gcp-6.2	—	6.2.0-1017.19~22.04.1
linux-gcp-fips	—	—
linux-gke	—	5.15.0-1045.50
linux-gke-4.15	—	—
linux-gke-5.15	—	—
linux-gke-5.4	—	—
linux-gkeop	—	5.15.0-1031.37
linux-gkeop-5.15	—	5.15.0-1031.37~20.04.1
linux-gkeop-5.4	—	—
linux-hwe	—	—
linux-hwe-5.11	—	—
linux-hwe-5.13	—	—
linux-hwe-5.15	—	5.15.0-87.97~20.04.1
linux-hwe-5.19	—	—
linux-hwe-5.4	—	5.4.0-165.182~18.04.1
linux-hwe-5.8	—	—
linux-hwe-6.2	—	6.2.0-35.35~22.04.1
linux-hwe-edge	—	—
linux-ibm	—	5.15.0-1041.44
linux-ibm-5.15	—	5.15.0-1041.44~20.04.1
linux-ibm-5.4	—	5.4.0-1059.64~18.04.1
linux-intel-5.13	—	—
linux-intel-iot-realtime	—	5.15.0-1041.43
linux-intel-iotg	—	5.15.0-1043.49
linux-intel-iotg-5.15	—	5.15.0-1043.49~20.04.1
linux-iot	—	5.4.0-1024.25
linux-kvm	—	5.15.0-1045.50
linux-lowlatency	—	5.15.0-87.96
linux-lowlatency-hwe-5.15	—	5.15.0-87.96~20.04.1
linux-lowlatency-hwe-5.19	—	—
linux-lowlatency-hwe-6.2	—	6.2.0-1015.15~22.04.1
linux-lts-xenial	—	4.4.0-246.280~14.04.1
linux-nvidia	—	5.15.0-1039.39
linux-nvidia-6.2	—	6.2.0-1011.11
linux-nvidia-6.5	—	6.5.0-1007.7
linux-nvidia-tegra	—	5.15.0-1019.19
linux-nvidia-tegra-5.15	—	5.15.0-1019.19~20.04.1
linux-nvidia-tegra-igx	—	5.15.0-1006.6
linux-oem	—	—
linux-oem-5.10	—	—
linux-oem-5.13	—	—
linux-oem-5.14	—	—
linux-oem-5.17	—	—
linux-oem-5.6	—	—
linux-oem-6.0	—	—
linux-oem-6.1	—	6.1.0-1025.25
linux-oem-6.5	—	6.5.0-1007.7
linux-oracle	—	5.15.0-1046.52
linux-oracle-5.0	—	—
linux-oracle-5.11	—	—
linux-oracle-5.13	—	—
linux-oracle-5.15	—	5.15.0-1046.52~20.04.1
linux-oracle-5.3	—	—
linux-oracle-5.4	—	5.4.0-1111.120~18.04.1
linux-oracle-5.8	—	—
linux-raspi	—	5.15.0-1041.44
linux-raspi-5.4	—	5.4.0-1096.107~18.04.1
linux-raspi-realtime	—	—
linux-raspi2	—	—
linux-realtime	—	5.15.0-1049.55
linux-riscv	—	—
linux-riscv-5.11	—	—
linux-riscv-5.15	—	5.15.0-1044.48~20.04.1
linux-riscv-5.19	—	—
linux-riscv-5.8	—	—
linux-starfive-5.19	—	—
linux-starfive-6.2	—	6.2.0-1007.8~22.04.1
linux-xilinx-zynqmp	—	5.15.0-1025.29

References

REPORT https://ubuntu.com/security/CVE-2023-4921

REPORT https://lore.kernel.org/all/[email protected]/

ADVISORY https://ubuntu.com/security/notices/USN-6439-1

ADVISORY https://ubuntu.com/security/notices/USN-6440-1

ADVISORY https://ubuntu.com/security/notices/USN-6441-1

ADVISORY https://ubuntu.com/security/notices/USN-6442-1

ADVISORY https://ubuntu.com/security/notices/USN-6444-1

ADVISORY https://ubuntu.com/security/notices/USN-6445-1

ADVISORY https://ubuntu.com/security/notices/USN-6446-1

ADVISORY https://ubuntu.com/security/notices/USN-6440-2

ADVISORY https://ubuntu.com/security/notices/USN-6439-2

ADVISORY https://ubuntu.com/security/notices/USN-6441-2

ADVISORY https://ubuntu.com/security/notices/USN-6444-2

ADVISORY https://ubuntu.com/security/notices/USN-6445-2

ADVISORY https://ubuntu.com/security/notices/USN-6446-2

ADVISORY https://ubuntu.com/security/notices/USN-6440-3

ADVISORY https://ubuntu.com/security/notices/USN-6446-3

ADVISORY https://ubuntu.com/security/notices/USN-6454-1

ADVISORY https://ubuntu.com/security/notices/USN-6441-3

ADVISORY https://ubuntu.com/security/notices/USN-6454-2

ADVISORY https://ubuntu.com/security/notices/USN-6461-1

ADVISORY https://ubuntu.com/security/notices/USN-6466-1

ADVISORY https://ubuntu.com/security/notices/USN-6454-3

ADVISORY https://ubuntu.com/security/notices/USN-6454-4

ADVISORY https://ubuntu.com/security/notices/USN-6479-1

ADVISORY https://ubuntu.com/security/notices/USN-6699-1

REPORT https://www.cve.org/CVERecord?id=CVE-2023-4921

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🛡️ CVE-2023-4921 on Ubuntu — linux

Description

Distribution advisory

How this vulnerability can be exploited

CVSS metrics in full

Weakness class

Affected software

Timeline and source

References

Other advisories for this package

Same weakness in other software

CVE-2023-4921 on other distributions

Is linux part of your stack?

Browse related advisories

Company

Resources

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