# CVE-2025-39857: Linux Kernel NULL pointer dereference in net/smc

Source: https://junglewise.ai/threats/cve-2025-39857-linux-kernel-null-pointer-dereference-in-net-smc  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-09-19. Updated: 2026-07-30  
License: CC BY 4.0 with a link back

CVE-2025-39857 · Severity: high · CVSS 7.5 · Published 2025-09-19

A vulnerability exists in the Linux kernel's Shared Memory Communications (SMC) protocol, which is used for high-performance data exchange. When using specific software-based network acceleration (RoCE), the system may encounter a critical error and crash. This can lead to a complete denial of service, impacting the availability of applications and services relying on these network protocols.

Technologies: [Linux Kernel](https://junglewise.ai/threats/technologies/kernel), [Siemens SIMATIC CN 4100](https://junglewise.ai/threats/technologies/simatic-cn-4100). Vendors: [Linux](https://junglewise.ai/threats/vendors/linux), [Siemens](https://junglewise.ai/threats/vendors/siemens).

## Quick answers

**Is CVE-2025-39857 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-39857 being exploited in the wild.

**How severe is CVE-2025-39857?** High severity, with a CVSS score of 7.5, published 19 September 2025.

**Which products and versions are affected?** Linux Kernel 6.0 to 6.1.151, 6.2 to 6.6.105, 6.7 to 6.12.46, 6.13 to 6.16.6, 6.17-rc1 to 6.17-rc4, 6.0 to 6.1.151, 6.6.105, 6.12.46, 6.16.6; Siemens SIMATIC CN 4100 before V5.0.

**Is there a fix for CVE-2025-39857?** A patch was published on 2025-08-28: Initial patch authored by Liu Jian Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2025-39857 attacked?** It is attacked over the network or with local access, in an operating system.

**Am I affected by CVE-2025-39857?** Check whether you run Linux Kernel or Siemens SIMATIC CN 4100 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A NULL pointer dereference vulnerability exists in the 'smc_ib_is_sg_need_sync()' function within the 'net/smc' subsystem of the Linux kernel. The issue occurs because the code fails to validate the 'ibdev->dma_device' pointer when a software RDMA over Converged Ethernet (RoCE) device is used. An attacker or specific network conditions triggering 'smc_listen_work' can cause a kernel panic (Oops), leading to a denial of service. The fix introduces a null pointer check for 'dma_device' before it is accessed. Patches have been released for multiple stable kernel branches including 6.1.y, 6.6.y, 6.12.y, and 6.16.y.

## Affected products

- Linux Linux Kernel 6.0 to 6.1.151, 6.6.105, 6.12.46, 6.16.6
- Siemens SIMATIC CN 4100 before V5.0

## Timeline

- 2025-08-28: patched: Initial patch authored by Liu Jian
- 2025-09-19: disclosed: CVE published

## References

- [https://git.kernel.org/stable/c/0cdf1fd8fc59d44a48c694324611136910301ef9](https://git.kernel.org/stable/c/0cdf1fd8fc59d44a48c694324611136910301ef9)
- [https://git.kernel.org/stable/c/34f17cbe027050b8d5316ea1b6f9bd7c378e92de](https://git.kernel.org/stable/c/34f17cbe027050b8d5316ea1b6f9bd7c378e92de)
- [https://git.kernel.org/stable/c/ba1e9421cf1a8369d25c3832439702a015d6b5f9](https://git.kernel.org/stable/c/ba1e9421cf1a8369d25c3832439702a015d6b5f9)
- [https://git.kernel.org/stable/c/eb929910bd4b4165920fa06a87b22cc6cae92e0e](https://git.kernel.org/stable/c/eb929910bd4b4165920fa06a87b22cc6cae92e0e)
- [https://git.kernel.org/stable/c/f18d9b3abf9c6587372cc702f963a7592277ed56](https://git.kernel.org/stable/c/f18d9b3abf9c6587372cc702f963a7592277ed56)
- [https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html](https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html)
- [https://cert-portal.siemens.com/productcert/html/ssa-032379.html](https://cert-portal.siemens.com/productcert/html/ssa-032379.html)

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