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Linux KernelOperating system · Linux

CVE-2021-20320

MEDIUM · 5.5 CVSS v3.1 Published 2022-02-18
Fix available
A fix is available. Upgrade to 5.15 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A flaw was found in s390 eBPF JIT in bpf_jit_insn in arch/s390/net/bpf_jit_comp.c in the Linux kernel. In this flaw, a local attacker with special user privilege can circumvent the verifier and may lead to a confidentiality problem.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

A flaw in the s390 (IBM System z) eBPF JIT compiler in the Linux kernel allows local attackers with special user privileges to circumvent the eBPF verifier through the bpf_jit_insn function in arch/s390/net/bpf_jit_comp.c, potentially leading to confidentiality issues.

MitigationApply the Linux kernel security update that patches the s390 eBPF JIT verifier bypass vulnerability.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:< 5.15= 5.15
FedoraOperating system
Affected:= 34
Enterprise LinuxOperating system
Affected:= 7.0= 8.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Verify system architecture is s390
    Run 'uname -m' or check /proc/cpuinfo for 's390x' architecture. This vulnerability only affects the IBM System z architecture.
    Affected if The system is not running on s390 (s390x) architecture, then it is not affected by this specific flaw.
  2. Check kernel version
    Run 'uname -r' or 'cat /proc/version' to get the running kernel version.
    Affected if Kernel version is 5.15 or later (5.15.x where x > 0), then the system is not affected. Versions < 5.15 and exactly 5.15 are affected.
  3. Determine if eBPF JIT is enabled
    Check kernel config for CONFIG_BPF_JIT and arch-specific CONFIG_S390_BPF_JIT, or check if /proc/sys/net/core/bpf_jit_enable is set to 1.
    Affected if The eBPF JIT compiler is not enabled (bpf_jit_enable = 0 or not compiled in), then the attack surface is not present even on vulnerable versions.
  4. Check distribution-specific kernel
    For Fedora: 'rpm -q kernel'. For RHEL: 'rpm -q kernel-uek' or 'uname -r' to verify the specific version against the affected Fedora 34 or RHEL 7.0/8.0 releases.
    Affected if Running Fedora 34 or RHEL 7.0/8.0 with the vendor-provided kernel that has not been patched, then it is likely affected.

The system is affected only if it runs on s390 architecture with an unpatched kernel version < 5.15 (or exactly 5.15) and has the eBPF JIT compiler enabled.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.15 or later
Fixed in 5.15
Interim mitigation

Apply the Linux kernel security update that patches the s390 eBPF JIT verifier bypass vulnerability.

Recommended fix High confidence

Linux Kernel 5.15 or later

  1. 1. Identify the current Linux kernel version using 'uname -r'
  2. 2. For s390 (IBM Z) systems, upgrade to kernel version 5.15 or later
  3. 3. On Fedora 34 systems, apply available kernel updates: 'dnf update kernel'
  4. 4. On RHEL/Enterprise Linux 7.0 and 8.0, apply vendor updates: 'yum update kernel' or 'dnf update kernel'
  5. 5. Reboot the system to load the new kernel
  6. 6. Verify the new kernel version is loaded: 'uname -r'
Caveat Minimal risk - this is a s390 architecture-specific eBPF JIT fix that should not affect most deployments

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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Scan for this in your stack

Free · runs locally
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-20320 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data