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Fencer Vulns
medium 4.7

CVE-2021-33624 json

In kernel/bpf/verifier.c in the Linux kernel before 5.12.13, a branch can be mispredicted (e.g., because of type confusion) and consequentl…

published 2021-06-23 5 y ago modified 2026-10-08 31 d ago also EUVD-2021-20301

cvss
4.7
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.9%
EPSS 0.9% chance of exploitation in 30 days, percentile 60%
public exploits
0
none known

Summary

In kernel/bpf/verifier.c in the Linux kernel before 5.12.13, a branch can be mispredicted (e.g., because of type confusion) and consequently an unprivileged BPF program can read arbitrary memory locations via a side-channel attack, aka CID-9183671af6db.

Patch / fix

  • linux linux_kernel 5.12.13
  • linux Debian 14, Debian 13, Debian 12 5.10.46-1

debian advisories DEBIAN-CVE-2021-33624

  • linux Ubuntu 20.04 LTS 5.4.0-88.99
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1057.60
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1053.57
  • linux-gke Ubuntu 20.04 LTS 5.4.0-1053.56
  • linux-ibm Ubuntu 20.04 LTS 5.4.0-1005.6
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1047.49
  • linux-azure Ubuntu 20.04 LTS 5.4.0-1059.62
  • linux-gkeop Ubuntu 20.04 LTS 5.4.0-1024.25

ubuntu advisories UBUNTU-CVE-2021-33624

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-syms SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +6 more 4.12.14-197.99.1
  • kernel-source SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +6 more 4.12.14-197.99.1
  • kernel-default SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +8 more 4.12.14-197.99.1
  • kernel-zfcpdump SLES 15 SP1-LTSS, Manager Server 4.0 4.12.14-197.99.1
  • kernel-obs-build SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +6 more 4.12.14-197.99.1
  • kernel-rt Real Time Module 15 SP2 5.3.18-42.2
  • oracleasm Real Time Module 15 SP2 2.0.8-1.3.1
  • lttng-modules Real Time Module 15 SP2 2.10.10-1.5.1

suse advisories SUSE-SU-2021:2427-1SUSE-SU-2021:2426-1SUSE-SU-2021:2422-1SUSE-SU-2021:2421-1SUSE-SU-2021:2352-1SUSE-SU-2021:2349-1

  • kernel-default openSUSE Leap 15.3 4.12.14-197.99.1
  • kernel-vanilla openSUSE Leap 15.3 4.12.14-197.99.1
  • kernel-kvmsmall openSUSE Leap 15.3 4.12.14-197.99.1
  • kernel-zfcpdump openSUSE Leap 15.3 4.12.14-197.99.1
  • kernel-64kb openSUSE Leap 15.3 5.3.18-59.13.1
  • kernel-syms openSUSE Leap 15.3 5.3.18-59.13.1
  • kernel-obs-qa openSUSE Leap 15.3 5.3.18-59.13.1
  • kernel-source openSUSE Leap 15.3 5.3.18-59.13.1

opensuse advisories openSUSE-SU-2021:2427-1openSUSE-SU-2021:2352-1openSUSE-SU-2021:2305-1

  • kernel CBL-Mariner 2.0 5.10.78.1-1

azure linux advisories AZL-6564

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

  • linux Arch Linux 5.12.13.arch1-1
  • linux-zen Arch Linux 5.12.13.zen1-1
  • linux-hardened Arch Linux 5.12.13.hardened1-1
  • linux-lts Arch Linux 5.10.46-1

arch linux advisories AVG-2094AVG-2095AVG-2096AVG-2097

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-2021-33624 updated cvss 4.7

kernel: Linux kernel BPF protection against speculative execution attacks can be bypassed to read arbitrary kernel memory

  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, kernel-alt, python-perf, +9 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    affected: workaround, no fix available
  • 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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
31 d ago

Exploit prediction

0.93% chance of exploitation in the next 30 days, higher than 60% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • openwall.com http://www.openwall.com/lists/oss-security/2021/06/21/1 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
NVD 2.0 4.7 AV:L/AC:M/Au:N/C:C/I:N/A:N

Classification

Weakness
  • CWE-843 Access of Resource Using Incompatible Type
Technology feeds

References

Sources

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.