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Linux KernelOperating system · Linux

CVE-2023-1206

MEDIUM · 5.7 CVSS v3.1 Published 2023-06-30
Fix available
A fix is available. Upgrade to 6.5 or later.
See remediation →
59/100
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 hash collision flaw was found in the IPv6 connection lookup table in the Linux kernel’s IPv6 functionality when a user makes a new kind of SYN flood attack. A user located in the local network or with a high bandwidth connection can increase the CPU usage of the server that accepts IPV6 connections up to 95%.

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 hash collision vulnerability in the Linux kernel's IPv6 connection lookup table allows remote attackers to cause CPU exhaustion (up to 95%) via a specialized SYN flood attack. The flaw exploits how IPv6 connection tracking handles lookup operations, allowing an attacker to trigger pathological hash collisions that consume excessive CPU resources.

MitigationUpdate the Linux kernel to a version containing the fix for this vulnerability. Network-side rate limiting of SYN packets and connection tracking limits can provide interim mitigation.

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:< 6.5
Enterprise LinuxOperating system
Affected:= 8.0= 9.0
FedoraOperating system
Affected:= 38

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
Adjacent
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

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. Check the running kernel version
    Run 'uname -r' to get the kernel version, or check '/proc/version'. Compare the version number to the affected range (Linux Kernel < 6.5).
    Affected if Kernel version is below 6.5 and the system uses IPv6 connection tracking.
  2. Determine if IPv6 is enabled on the system
    Run 'ip -6 addr show' or check if /proc/sys/net/ipv6/ exists. Also run 'lsmod | grep ip6' to see if IPv6-related modules are loaded.
    Affected if IPv6 is enabled and the kernel version is in the affected range.
  3. Verify if IPv6 connection tracking is active
    Run 'lsmod | grep nf_conntrack_ipv6' or check 'cat /proc/net/stat/nf_conntrack' for IPv6 entries. The module 'nf_conntrack_ipv6' must be loaded for this vulnerability to be exploitable.
    Affected if The nf_conntrack_ipv6 module is loaded and the kernel version is vulnerable.
  4. Check connection tracking hash parameters
    Inspect '/proc/sys/net/netfilter/nf_conntrack_htable_size' (if available) or look at connection tracking limits via 'conntrack -L -s ::' to observe the hash table behavior under load.
    Affected if The system has a small connection tracking hash table or shows high CPU usage during IPv6 SYN traffic processing.

The system is affected if it runs a Linux kernel below version 6.5 with IPv6 and the nf_conntrack_ipv6 module enabled, and exhibits high CPU usage during IPv6 SYN flood traffic.

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 6.5 or later
Fixed in 6.5
Interim mitigation

Update the Linux kernel to a version containing the fix for this vulnerability. Network-side rate limiting of SYN packets and connection tracking limits can provide interim mitigation.

Recommended fix Moderate confidence

Linux Kernel 6.5 or later; or distribution-specific kernel update

  1. 1. Identify the current kernel version running on the affected system using 'uname -r'
  2. 2. For Linux Kernel: Upgrade to kernel version 6.5 or later which contains the fix for the IPv6 connection lookup table hash collision
  3. 3. For Red Hat Enterprise Linux 8.0/9.0: Apply the latest kernel updates from Red Hat's security channels using 'dnf update kernel' or 'yum update kernel'
  4. 4. For Fedora 38: Apply the latest kernel updates using 'dnf update kernel'
  5. 5. Reboot the system to load the new kernel
  6. 6. Verify the new kernel version is running with 'uname -r'
Caveat Kernel upgrades may require system reboot and could have compatibility implications with custom modules or specific hardware drivers

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
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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Scan for this in your stack

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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-2023-1206 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