high 7.8

CVE-2021-33033 json

The Linux kernel before 5.11.14 has a use-after-free in cipso_v4_genopt in net/ipv4/cipso_ipv4.c because the CIPSO and CALIPSO refcounting…

published 2021-05-14 5 y ago modified 2026-08-05 3 mo ago also EUVD-2021-19753

cvss: 7.8; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.6%; EPSS 0.6% chance of exploitation in 30 days, percentile 47%
public exploits: 0; none known

The Linux kernel before 5.11.14 has a use-after-free in cipso_v4_genopt in net/ipv4/cipso_ipv4.c because the CIPSO and CALIPSO refcounting for the DOI definitions is mishandled, aka CID-ad5d07f4a9cd. This leads to writing an arbitrary value.

Patch / fix

fixed in 1 distros 6 links 4

linux linux_kernel 4.9.298, 4.14.226, 4.19.181, 5.4.106, 5.10.24, 5.11.7

debian ubuntu red hat suse opensuse azure linux

linux Debian 14, Debian 13, Debian 12 5.10.24-1

debian advisories DEBIAN-CVE-2021-33033

linux Ubuntu 18.04 LTS 4.15.0-144.148
linux Ubuntu 20.04 LTS 5.4.0-73.82
linux-aws Ubuntu 18.04 LTS 4.15.0-1103.110
linux-aws Ubuntu 20.04 LTS 5.4.0-1048.50
linux-gcp Ubuntu 20.04 LTS 5.4.0-1043.46
linux-gke Ubuntu 20.04 LTS 5.4.0-1043.45
linux-kvm Ubuntu 18.04 LTS 4.15.0-1092.94
linux-kvm Ubuntu 20.04 LTS 5.4.0-1039.40

ubuntu advisories UBUNTU-CVE-2021-33033

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

kernel RHEL 8 4.18.0-348.el8
perf RHEL 8 4.18.0-348.el8
bpftool RHEL 8 4.18.0-348.el8
kernel-core RHEL 8 4.18.0-348.el8
kernel-tools RHEL 8 4.18.0-348.el8
python3-perf RHEL 8 4.18.0-348.el8
kernel-modules RHEL 8 4.18.0-348.el8
kernel-zfcpdump RHEL 8 4.18.0-348.el8

red hat advisories RHSA-2021:4356 RHSA-2021:4140 RHSA-2021:2725 RHSA-2021:2726

kernel-syms SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.78.1
kernel-source SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.78.1
kernel-default SLES for SAP 15, SLES 15-LTSS, SLE Live Patching 15 +3 more 4.12.14-150.78.1
kernel-vanilla SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.78.1
kernel-obs-build SLES for SAP 15, SLES 15-LTSS, SLE High Performance Computing 15-LTSS +1 more 4.12.14-150.78.2
kernel-syms SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +3 more 4.4.180-94.150.1
kernel-source SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +3 more 4.4.180-94.150.1
kernel-default SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +4 more 4.4.180-94.150.1

suse advisories SUSE-SU-2021:3969-1 SUSE-SU-2021:3935-1 SUSE-SU-2021:3929-1 SUSE-SU-2021:3876-1 SUSE-SU-2021:14849-1 SUSE-SU-2021:3748-1

kernel-default openSUSE Leap 15.3 4.12.14-197.102.2
kernel-vanilla openSUSE Leap 15.3 4.12.14-197.102.2
kernel-kvmsmall openSUSE Leap 15.3 4.12.14-197.102.2
kernel-zfcpdump openSUSE Leap 15.3 4.12.14-197.102.2
dtb-aarch64 openSUSE Leap 15.3 5.3.18-59.34.1
kernel-64kb openSUSE Leap 15.3 5.3.18-59.34.1
kernel-syms openSUSE Leap 15.3 5.3.18-59.34.1
kernel-obs-qa openSUSE Leap 15.3 5.3.18-59.34.1

opensuse advisories openSUSE-SU-2021:3876-1 openSUSE-SU-2021:3675-1 openSUSE-SU-2021:1477-1 openSUSE-SU-2021:3641-1

kernel CBL-Mariner 2.0 5.10.78.1-1

azure linux advisories AZL-6561

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-33033 updated 2026-11-07 cvss 7.8

kernel: use-after-free in cipso_v4_genopt in net/ipv4/cipso_ipv4.c

Red Hat Enterprise Linux 7 perf, kernel, kernel-alt, python-perf, kernel-kdump, kernel-tools, +3 more
affected: workaround, no fix planned “Will not fix”
Red Hat CodeReady Linux Builder (v. 8) kernel-debuginfo-common-x86_64 4.18.0-348.el8, kernel-debuginfo-common-aarch64 4.18.0-348.el8, kernel-debuginfo-common-ppc64le 4.18.0-348.el8 Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-348.el8, kernel 4.18.0-348.el8, bpftool 4.18.0-348.el8, kernel-core 4.18.0-348.el8, kernel-tools 4.18.0-348.el8, python3-perf 4.18.0-348.el8, +15 more
fixed: vendor fix RHSA-2021:4356
Red Hat Enterprise Linux Client (v. 7) perf 3.10.0-1160.36.2.el7, kernel 3.10.0-1160.36.2.el7, bpftool 3.10.0-1160.36.2.el7, python-perf 3.10.0-1160.36.2.el7, kernel-tools 3.10.0-1160.36.2.el7, kernel-tools-libs 3.10.0-1160.36.2.el7, +2 more Red Hat Enterprise Linux Client Optional (v. 7) kernel-debuginfo-common-x86_64 3.10.0-1160.36.2.el7 Red Hat Enterprise Linux ComputeNode Optional (v. 7) kernel-debuginfo-common-x86_64 3.10.0-1160.36.2.el7
fixed: vendor fix RHSA-2021:2725
Red Hat Enterprise Linux for Real Time (v. 7) kernel-rt 3.10.0-1160.36.2.rt56.1179.el7, kernel-rt-trace 3.10.0-1160.36.2.rt56.1179.el7, kernel-rt-debuginfo-common-x86_64 3.10.0-1160.36.2.rt56.1179.el7 Red Hat Enterprise Linux for Real Time for NFV (v. 7) kernel-rt 3.10.0-1160.36.2.rt56.1179.el7, kernel-rt-kvm 3.10.0-1160.36.2.rt56.1179.el7, kernel-rt-trace 3.10.0-1160.36.2.rt56.1179.el7, kernel-rt-debug-kvm 3.10.0-1160.36.2.rt56.1179.el7, kernel-rt-trace-kvm 3.10.0-1160.36.2.rt56.1179.el7, kernel-rt-debuginfo-common-x86_64 3.10.0-1160.36.2.rt56.1179.el7
fixed: vendor fix RHSA-2021:2726
Red Hat Enterprise Linux Real Time (v. 8) kernel-rt 4.18.0-348.rt7.130.el8, kernel-rt-core 4.18.0-348.rt7.130.el8, kernel-rt-modules 4.18.0-348.rt7.130.el8, kernel-rt-debug-core 4.18.0-348.rt7.130.el8, kernel-rt-debug-modules 4.18.0-348.rt7.130.el8, kernel-rt-modules-extra 4.18.0-348.rt7.130.el8, +2 more Red Hat Enterprise Linux Real Time for NFV (v. 8) kernel-rt 4.18.0-348.rt7.130.el8, kernel-rt-kvm 4.18.0-348.rt7.130.el8, kernel-rt-core 4.18.0-348.rt7.130.el8, kernel-rt-modules 4.18.0-348.rt7.130.el8, kernel-rt-debug-kvm 4.18.0-348.rt7.130.el8, kernel-rt-debug-core 4.18.0-348.rt7.130.el8, +4 more
fixed: vendor fix RHSA-2021:4140
Red Hat Enterprise Linux Server (v. 7) perf 3.10.0-1160.36.2.el7, kernel 3.10.0-1160.36.2.el7, bpftool 3.10.0-1160.36.2.el7, python-perf 3.10.0-1160.36.2.el7, kernel-kdump 3.10.0-1160.36.2.el7, kernel-tools 3.10.0-1160.36.2.el7, +7 more Red Hat Enterprise Linux Server Optional (v. 7) kernel-debuginfo-common-ppc64 3.10.0-1160.36.2.el7, kernel-debuginfo-common-x86_64 3.10.0-1160.36.2.el7, kernel-debuginfo-common-ppc64le 3.10.0-1160.36.2.el7 Red Hat Enterprise Linux Workstation (v. 7) perf 3.10.0-1160.36.2.el7, kernel 3.10.0-1160.36.2.el7, bpftool 3.10.0-1160.36.2.el7, python-perf 3.10.0-1160.36.2.el7, kernel-tools 3.10.0-1160.36.2.el7, kernel-tools-libs 3.10.0-1160.36.2.el7, +2 more Red Hat Enterprise Linux Workstation Optional (v. 7) kernel-debuginfo-common-x86_64 3.10.0-1160.36.2.el7
fixed: vendor fix RHSA-2021:2725
Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.57% chance of exploitation in the next 30 days, higher than 47% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

syzkaller.appspot.com https://syzkaller.appspot.com/bug?id=96e7d345748d8814901c91cd92084ed04b46701e referenced PoC, tagged "exploit" by a source, unverified
sites.google.com https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-cipso_v4_genopt referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	7.8	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD	2.0	4.6	AV:L/AC:L/Au:N/C:P/I:P/A:P

Classification

Weakness

CWE-416 Use After Free

Technology feeds

Linux kernel rss critical rss

References

git.kernel.org /pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ad5d07f4a9cd671233ae20983848874731102c08
mailing-list, patch, vendor-advisory
git.kernel.org /pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1165affd484889d4986cf3b724318935a0b120d8
mailing-list, patch, vendor-advisory
cdn.kernel.org /pub/linux/kernel/v5.x/ChangeLog-5.11.7
mailing-list, patch, vendor-advisory
cdn.kernel.org /pub/linux/kernel/v5.x/ChangeLog-5.11.14
mailing-list, patch, vendor-advisory
syzkaller.appspot.com /bug?id=96e7d345748d8814901c91cd92084ed04b46701e
exploit, mailing-list, third-party-advisory
sites.google.com /view/syzscope/kasan-use-after-free-read-in-cipso_v4_genopt
exploit, third-party-advisory

Sources

CVE List CVE-2021-33033
NVD CVE-2021-33033

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary