UBUNTU-CVE-2025-40300
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 ]
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
44 explicit affected versions
108 explicit affected versions
74 explicit affected versions
50 explicit affected versions
6 explicit affected versions
12 explicit affected versions
19 explicit affected versions
6 explicit affected versions
84 explicit affected versions
57 explicit affected versions
24 explicit affected versions
69 explicit affected versions
69 explicit affected versions
82 explicit affected versions
76 explicit affected versions
64 explicit affected versions
10 explicit affected versions
24 explicit affected versions
26 explicit affected versions
76 explicit affected versions
183 explicit affected versions
7 explicit affected versions
73 explicit affected versions
28 explicit affected versions
13 explicit affected versions
77 explicit affected versions
31 explicit affected versions
35 explicit affected versions
36 explicit affected versions
34 explicit affected versions
18 explicit affected versions
32 explicit affected versions
108 explicit affected versions
64 explicit affected versions
33 explicit affected versions
112 explicit affected versions
13 explicit affected versions
4 explicit affected versions
23 explicit affected versions
113 explicit affected versions
39 explicit affected versions
115 explicit affected versions
1 explicit affected versions
1 explicit affected versions
21 explicit affected versions
9 explicit affected versions
16 explicit affected versions
10 explicit affected versions
66 explicit affected versions
35 explicit affected versions
8 explicit affected versions
7 explicit affected versions
12 explicit affected versions
8 explicit affected versions
7 explicit affected versions
12 explicit affected versions
14 explicit affected versions
10 explicit affected versions
1 explicit affected versions
7 explicit affected versions
5 explicit affected versions
97 explicit affected versions
12 explicit affected versions
98 explicit affected versions
12 explicit affected versions
28 explicit affected versions
112 explicit affected versions
30 explicit affected versions
10 explicit affected versions
22 explicit affected versions
21 explicit affected versions
10 explicit affected versions
180 explicit affected versions
37 explicit affected versions
8 explicit affected versions
13 explicit affected versions
27 explicit affected versions
3 explicit affected versions
10 explicit affected versions
8 explicit affected versions
51 explicit affected versions
1 explicit affected versions
26 explicit affected versions
2 explicit affected versions
13 explicit affected versions
23 explicit affected versions
1 explicit affected versions
29 explicit affected versions
102 explicit affected versions
13 explicit affected versions
9 explicit affected versions
81 explicit affected versions
28 explicit affected versions
28 explicit affected versions
1 explicit affected versions
93 explicit affected versions
76 explicit affected versions
39 explicit affected versions
33 explicit affected versions
23 explicit affected versions
45 explicit affected versions
10 explicit affected versions
7 explicit affected versions
6 explicit affected versions
106 explicit affected versions
11 explicit affected versions
5 explicit affected versions
12 explicit affected versions
129 explicit affected versions
7 explicit affected versions
12 explicit affected versions
2 explicit affected versions
4 explicit affected versions
61 explicit affected versions
121 explicit affected versions
77 explicit affected versions
157 explicit affected versions
143 explicit affected versions
10 explicit affected versions
26 explicit affected versions
30 explicit affected versions
1 explicit affected versions
53 explicit affected versions
22 explicit affected versions
34 explicit affected versions
8 explicit affected versions
13 explicit affected versions
33 explicit affected versions
129 explicit affected versions
70 explicit affected versions
16 explicit affected versions
76 explicit affected versions
37 explicit affected versions
3 explicit affected versions
123 explicit affected versions
83 explicit affected versions
1 explicit affected versions
7 explicit affected versions
2 explicit affected versions
51 explicit affected versions
82 explicit affected versions
18 explicit affected versions
29 explicit affected versions
12 explicit affected versions
64 explicit affected versions
64 explicit affected versions
27 explicit affected versions
50 explicit affected versions
112 explicit affected versions
1 explicit affected versions
1 explicit affected versions
87 explicit affected versions
30 explicit affected versions
8 explicit affected versions
41 explicit affected versions
5 explicit affected versions
3 explicit affected versions
8 explicit affected versions
1 explicit affected versions
10 explicit affected versions
7 explicit affected versions
33 explicit affected versions
13 explicit affected versions
101 explicit affected versions
13 explicit affected versions
64 explicit affected versions
7 explicit affected versions
8 explicit affected versions
84 explicit affected versions
10 explicit affected versions
12 explicit affected versions
6 explicit affected versions
24 explicit affected versions
100 explicit affected versions
73 explicit affected versions
47 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
38 explicit affected versions
14 explicit affected versions
38 explicit affected versions
9 explicit affected versions
11 explicit affected versions
26 explicit affected versions
9 explicit affected versions
77 explicit affected versions
8 explicit affected versions
7 explicit affected versions
89 explicit affected versions
133 explicit affected versions
112 explicit affected versions
4 explicit affected versions
66 explicit affected versions
1 explicit affected versions
1 explicit affected versions
1 explicit affected versions
75 explicit affected versions
103 explicit affected versions
66 explicit affected versions
65 explicit affected versions
13 explicit affected versions
43 explicit affected versions
68 explicit affected versions
136 explicit affected versions
110 explicit affected versions
157 explicit affected versions
10 explicit affected versions
8 explicit affected versions
32 explicit affected versions
80 explicit affected versions
14 explicit affected versions
4 explicit affected versions
78 explicit affected versions
11 explicit affected versions
1 explicit affected versions
59 explicit affected versions
114 explicit affected versions
6 explicit affected versions
26 explicit affected versions
65 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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 ]
05 / REFERENCES
Further evidence
- https://comsec-files.ethz.ch/papers/vmscape_sp26.pdf
- https://comsec.ethz.ch/research/microarch/vmscape-exposing-and-exploiting-incomplete-branch-predictor-isolation-in-cloud-environments/
- https://lore.kernel.org/all/2025091125-clustered-tractor-13c0@gregkh/
- https://ubuntu.com/security/CVE-2025-40300
- https://ubuntu.com/security/notices/USN-7850-1
- https://ubuntu.com/security/notices/USN-7853-1
- https://ubuntu.com/security/notices/USN-7853-2
- https://ubuntu.com/security/notices/USN-7853-3
- https://ubuntu.com/security/notices/USN-7854-1
- https://ubuntu.com/security/notices/USN-7860-1
- https://ubuntu.com/security/notices/USN-7860-2
- https://ubuntu.com/security/notices/USN-7860-3
- https://ubuntu.com/security/notices/USN-7860-4
- https://ubuntu.com/security/notices/USN-7860-5
- https://ubuntu.com/security/notices/USN-7861-1
- https://ubuntu.com/security/notices/USN-7861-2
- https://ubuntu.com/security/notices/USN-7861-3
- https://ubuntu.com/security/notices/USN-7861-5
- https://ubuntu.com/security/notices/USN-7862-1
- https://ubuntu.com/security/notices/USN-7862-2
- https://ubuntu.com/security/notices/USN-7862-3
- https://ubuntu.com/security/notices/USN-7863-1
- https://ubuntu.com/security/notices/USN-7864-1
- https://ubuntu.com/security/notices/USN-7865-1
- https://ubuntu.com/security/notices/USN-7874-1
- https://ubuntu.com/security/notices/USN-7874-2
- https://ubuntu.com/security/notices/USN-7874-3
- https://ubuntu.com/security/notices/USN-7910-1
- https://ubuntu.com/security/notices/USN-7910-2
- https://ubuntu.com/security/notices/USN-7933-1
- https://ubuntu.com/security/notices/USN-7934-1
- https://ubuntu.com/security/notices/USN-7935-1
- https://ubuntu.com/security/notices/USN-7937-1
- https://ubuntu.com/security/notices/USN-7938-1
- https://ubuntu.com/security/notices/USN-7939-1
- https://ubuntu.com/security/notices/USN-7939-2
- https://ubuntu.com/security/notices/USN-7940-1
- https://ubuntu.com/security/notices/USN-7940-2
- https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7046.html
- https://www.cve.org/CVERecord?id=CVE-2025-40300
- https://www.intel.com/content/www/us/en/developer/articles/news/more-information-vmscape.html
- https://www.theregister.com/2025/09/11/vmscape_spectre_vulnerability/