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CVE-2025-21959 high CVSS 7.3

Vulnerability in Linux kernel (CVE-2025-21959)

Summary

Vulnerability in Linux kernel (CVE-2025-21959). Risk of unauthorized operations or information disclosure. Exploitable via cpu.

Original description

The description as published by the source.

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

netfilter: nf_conncount: Fully initialize struct nf_conncount_tuple in insert_tree()

Since commit b36e4523d4d5 ("netfilter: nf_conncount: fix garbage
collection confirm race"), cpu and jiffies32 were introduced to
the struct nf_conncount_tuple.

The commit made nf_conncount_add() initialize conn->cpu and
conn->jiffies32 when allocating the struct.
In contrast, count_tree() was not changed to initialize them.

By commit 34848d5c896e ("netfilter: nf_conncount: Split insert and
traversal"), count_tree() was split and the relevant allocation
code now resides in insert_tree().
Initialize conn->cpu and conn->jiffies32 in insert_tree().

BUG: KMSAN: uninit-value in find_or_evict net/netfilter/nf_conncount.c:117 [inline]
BUG: KMSAN: uninit-value in __nf_conncount_add+0xd9c/0x2850 net/netfilter/nf_conncount.c:143
find_or_evict net/netfilter/nf_conncount.c:117 [inline]
__nf_conncount_add+0xd9c/0x2850 net/netfilter/nf_conncount.c:143
count_tree net/netfilter/nf_conncount.c:438 [inline]
nf_conncount_count+0x82f/0x1e80 net/netfilter/nf_conncount.c:521
connlimit_mt+0x7f6/0xbd0 net/netfilter/xt_connlimit.c:72
__nft_match_eval net/netfilter/nft_compat.c:403 [inline]
nft_match_eval+0x1a5/0x300 net/netfilter/nft_compat.c:433
expr_call_ops_eval net/netfilter/nf_tables_core.c:240 [inline]
nft_do_chain+0x426/0x2290 net/netfilter/nf_tables_core.c:288
nft_do_chain_ipv4+0x1a5/0x230 net/netfilter/nft_chain_fil…

Source: NIST National Vulnerability Database 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-2025-21959 has been found in Linux kernel.
Attackers can target a specific entry point like cpu over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.3/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2025-21959" on the vendor's site.

CVE-2025-21959 (Linux kernel) — CWE-908 / CVSS v3 7.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: cpu / jiffies32
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-908) exists in Linux kernel. Attackers reach the vulnerable code path via cpu without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of Linux kernel. Attack surface: cpu / jiffies32.

🔥 Severity

Severity: High (CVSS 7.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to the patched release per vendor advisory.

🛡️ 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. Audit SBOM/dependencies to find affected services.

Response actions

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

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで Linux kernel を使っているサービスとバージョンを洗い出す。

  2. 2
    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":"4.18.0"},{"fixed":"5.4.292"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.5.0"},{"fixed":"5.10.236"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.180"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.132"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.84"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.20"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.13.8"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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