🛡️ CVE-2025-40300 on Debian — linux

⚪ Unknown ✅ No Known Exploit OSV

N/A

CVSS Score

0 Low4 Medium7 High9 Critical10

Description

In the Linux kernel, the following vulnerability has been resolved: x86/vmscape: Add conditional IBPB mitigation VMSCAPE is a vulnerability that exploits insufficient branch predictor isolation between a guest and a userspace hypervisor (like QEMU). Existing mitigations already protect kernel/KVM from a malicious guest. Userspace can additionally be protected by flushing the branch predictors after a VMexit. Since it is the userspace that consumes the poisoned branch predictors, conditionally issue an IBPB after a VMexit and before returning to userspace. Workloads that frequently switch between hypervisor and userspace will incur the most overhead from the new IBPB. This new IBPB is not integrated with the existing IBPB sites. For instance, a task can use the existing speculation control prctl() to get an IBPB at context switch time. With this implementation, the IBPB is doubled up: one at context switch and another before running userspace. The intent is to integrate and optimize these cases post-embargo. [ dhansen: elaborate on suboptimal IBPB solution ]

Distribution advisory

This page covers CVE-2025-40300 as tracked by Debian, for the package linux. The fix is available in version 6.16.7-1; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

Affected software

DEBIAN-CVE-2025-40300 is recorded against 2 packages.

linux (fixed in 6.16.7-1)
linux-6.1 (fixed in 6.1.153-1~deb11u1)

Timeline and source

Published on 11 September 2025 and last revised on 4 August 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

security-tracker.debian.org (Advisory)

CVE-2025-40300 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

BellSoft Base record Debian 11 (Root.io)Debian 12 (Root.io)Debian 13 (Root.io)Ubuntu 22.04 (Root.io)Ubuntu 24.04 (Root.io)Ubuntu

Details

Severity Unknown

CVSS Score N/A

CVSS Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CWE N/A

Public Exploit ✅ No

Source OSV

Published 2025-09-11

Updated 2026-08-20

Modified 2026-08-04

Fix URL N/A

Affected Packages

Software	From version	Fixed in
linux	—	6.16.7-1
linux-6.1	—	6.1.153-1~deb11u1

References

ADVISORY https://security-tracker.debian.org/tracker/CVE-2025-40300

🔗 NVD 🔗 Mitre

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