CVE Intelligence
Medium

CVE-2025-40300 — x86/vmscape: Add conditional IBPB mitigation

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 ]

Published Sep 11, 2025 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Linux

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.4% (30-day exploitation probability)+4
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.35%
ahead of 27% of scored CVEs · Oct 14, 2026
Affects
Debian
Debian Linux and 2 more
CVSS base
5.5
Medium · 1 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Linux Linux, Linux Linux Kernel).
  2. Apply the fixed version or the patch documented under Remediation.
  3. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Debian Debian Linux version 11.0 Vulnerable NIST National Vulnerability Database
Linux Linux ≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < 510603f504796c3535f67f55fb0b124a303b44c8≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < 2f4f2f8f860cb4c3336a7435ebe8dcfded0c9c6e≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < 15006289e5c38b2a830e1fba221977a27598176c≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < 893387c18612bb452336a5881da0d015a7e8f4a2≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < f866eef8d1c65504d30923c3f14082ad294d0e6d≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < 34e5667041050711a947e260fc9ebebe08bddee5≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < d7ddc93392e4a7ffcccc86edf6ef3e64c778db52≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < 459274c77b37ac63b78c928b4b4e748d1f9d05c8
and 10 more ≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < d5490dfa35427a2967e00a4c7a1b95fdbc8ede34≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < 9c23a90648e831d611152ac08dbcd1283d405e7f≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < 2f8f173413f1cbf52660d04df92d0069c4306d25version c51f1e5f57cca88d8d5894b6fad1638f643a99d0version 4b3870c343a82cd2df7192cc5149c87205dcc611≥ 3.16.57 and < 3.17≥ 4.4.168 and < 4.5version 4.16≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < c08192b5d6730a914dee6175bc71092ee6a65f14≥ 15d45071523d89b3fb7372e2135fbd72f6af9506 and < ac60717f9a8d21c58617d0b34274babf24135835
Vulnerable CVE Program (cve.org) e CISA ADP
Linux Linux Kernel version 6.17-rc5version 6.17-rc4version 6.17-rc3version 6.17-rc2version 6.17-rc1≥ 6.13 and < 6.16.7≥ 6.7 and < 6.12.47≥ 6.2 and < 6.6.106
and 5 more ≥ 5.16 and < 6.1.152≥ 5.11 and < 5.15.193≥ 4.16 and < 5.10.244≥ 4.4.168 and < 4.5≥ 3.16.57 and < 3.17
Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
5.5 CVSS 3.1 Medium 1.8 3.6 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · linux/linux
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 15, 2026
  • Fix documented
    Oct 15, 2026 · NIST National Vulnerability Database
  • CVSS changed · 5.5
    Oct 15, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 15, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 15, 2026 · NIST National Vulnerability Database
  • 2025
  • CVE published
    Sep 11, 2025 · Linux

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

23 on the record

Elsewhere on this site

Debian
every CVE for this vendor

Related CVEs (same products)

  • CVE-2026-99999 ipv4: validate checksum_start before completing checksum 9h
  • CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 9h
  • CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
  • CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
  • CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
  • CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No CWE classification.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2025-40300 is "x86/vmscape: Add conditional IBPB mitigation", rated Medium. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.5 describes technical severity. EPSS 0.35% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.

Sign in or create an account to comment and suggest corrections.