{"id":"CVE-2026-23553","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-23553","generatedAt":"2026-10-28T07:26:14.674Z","title":"In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run.","description":"In the context switch logic Xen attempts to skip an IBPB in the case of\na vCPU returning to a CPU on which it was the previous vCPU to run.\nWhile safe for Xen's isolation between vCPUs, this prevents the guest\nkernel correctly isolating between tasks.  Consider:\n\n 1) vCPU runs on CPU A, running task 1.\n 2) vCPU moves to CPU B, idle gets scheduled on A.  Xen skips IBPB.\n 3) On CPU B, guest kernel switches from task 1 to 2, issuing IBPB.\n 4) vCPU moves back to CPU A.  Xen skips IBPB again.\n\nNow, task 2 is running on CPU A with task 1's training still in the BTB.","published":"2026-01-28T16:16:17.000Z","lastModified":"2026-06-17T10:21:46.000Z","status":"Analyzed","sourceIdentifier":"security@xen.org","cvss":{"version":"3.1","score":2.9,"severity":"LOW","vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"},"cwe":["CWE-665","CWE-693"],"affected":["xen/xen"],"epss":{"score":0.00145,"percentile":0.03724,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.14%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://xenbits.xenproject.org/xsa/advisory-479.html","tags":["Mitigation","Patch","Vendor Advisory"],"source":"security@xen.org"},{"url":"http://www.openwall.com/lists/oss-security/2026/01/27/3","tags":["Mailing List","Mitigation","Patch","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"http://xenbits.xen.org/xsa/advisory-479.html","tags":["Mitigation","Patch","Vendor Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-23553","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}