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CVE-2025-39684 medium CVSS 5.5

Vulnerability in Linux kernel (CVE-2025-39684)

Summary

Vulnerability in Linux kernel (CVE-2025-39684). Risk of unauthorized operations or information disclosure. Exploitable via INSN_READ.

Original description

The description as published by the source.

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

comedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()

syzbot reports a KMSAN kernel-infoleak in do_insn_ioctl(). A kernel
buffer is allocated to hold insn->n samples (each of which is an
unsigned int). For some instruction types, insn->n samples are
copied back to user-space, unless an error code is being returned. The
problem is that not all the instruction handlers that need to return
data to userspace fill in the whole insn->n samples, so that there is
an information leak. There is a similar syzbot report for
do_insnlist_ioctl(), although it does not have a reproducer for it at
the time of writing.

One culprit is insn_rw_emulate_bits() which is used as the handler for
INSN_READ or INSN_WRITE instructions for subdevices that do not have
a specific handler for that instruction, but do have an INSN_BITS
handler. For INSN_READ it only fills in at most 1 sample, so if
insn->n is greater than 1, the remaining insn->n - 1 samples copied
to userspace will be uninitialized kernel data.

Another culprit is vm80xx_ai_insn_read() in the "vm80xx" driver. It
never returns an error, even if it fails to fill the buffer.

Fix it in do_insn_ioctl() and do_insnlist_ioctl() by making sure
that uninitialized parts of the allocated buffer are zeroed before
handling each instruction.

Thanks to Arnaud Lecomte for their fix to do_insn_ioctl(). That fix
repla…

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-2025-39684 has been found in Linux kernel.
Attackers can target a specific entry point like INSN_READ over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.5/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2025-39684" on the vendor's site.

CVE-2025-39684 (Linux kernel) — CWE-908 / CVSS v3 5.5
Attack vector: local / no user interaction
Attack surface: INSN_READ / INSN_WRITE / INSN_BITS
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 INSN_READ.

📍 Affected scope

Check the vendor advisory for the affected versions of Linux kernel. Attack surface: INSN_READ / INSN_WRITE / INSN_BITS.

🔥 Severity

Severity: Medium (CVSS 5.5/10). 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":"2.6.29"},{"fixed":"5.15.190"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.149"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.103"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.44"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.16.4"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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