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CVE-2026-23300 medium CVSS 5.5

Vulnerability in Kernel (CVE-2026-23300)

Summary

Vulnerability in Kernel (CVE-2026-23300). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7 or later.

Original description

The description as published by the source.

In the Linux kernel, the following vulnerability has been resolved:

net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop

When a standalone IPv6 nexthop object is created with a loopback device
(e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies
it as a reject route. This is because nexthop objects have no destination
prefix (fc_dst=::), causing fib6_is_reject() to match any loopback
nexthop. The reject path skips fib_nh_common_init(), leaving
nhc_pcpu_rth_output unallocated. If an IPv4 route later references this
nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and
panics.

Simplify the check in fib6_nh_init() to only match explicit reject
routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback
promotion heuristic in fib6_is_reject() is handled separately by
ip6_route_info_create_nh(). After this change, the three cases behave
as follows:

  1. Explicit reject route ("ip -6 route add unreachable 2001:db8::/64"):
    RTF_REJECT is set, enters reject path, skips fib_nh_common_init().
    No behavior change.

  2. Implicit loopback reject route ("ip -6 route add 2001:db8::/32 dev lo"):
    RTF_REJECT is not set, takes normal path, fib_nh_common_init() is
    called. ip6_route_info_create_nh() still promotes it to reject
    afterward. nhc_pcpu_rth_output is allocated but unused, which is
    harmless.

  3. Standalone nexthop object ("ip -6 nexthop add id 100 dev lo"):
    RTF_REJECT is not set, takes normal path, fib_nh_com…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-23300 has been found in Kernel.
Risk of unauthorized operations or information disclosure. CVSS score: 5.5/10.
What to do: upgrade Kernel to 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7 or later.
If unsure, ask your IT team or search "Kernel CVE-2026-23300" on the vendor's site.

CVE-2026-23300 (Kernel) — CWE-476 / CVSS v3 5.5
Attack vector: local / no user interaction
Patched: 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-476) exists in Kernel.

📍 Affected scope

Check the vendor advisory for the affected versions of Kernel.

🔥 Severity

Severity: Medium (CVSS 5.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Kernel' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'Kernel' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で Kernel を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade Kernel to 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7

    ステージング環境で 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

Linux Kernel
[{"type":"ECOSYSTEM","events":[{"introduced":"5.3.0"},{"fixed":"5.10.253"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.203"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.167"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.130"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.77"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.17"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.7"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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