{"id":"ALPINE-CVE-2026-23553","details":"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.","modified":"2026-01-29T11:30:45.163530Z","published":"2026-01-28T16:16:16.853Z","upstream":["CVE-2026-23553"],"references":[{"type":"ADVISORY","url":"https://security.alpinelinux.org/vuln/CVE-2026-23553"}],"affected":[{"package":{"name":"xen","ecosystem":"Alpine:v3.20","purl":"pkg:apk/alpine/xen?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.18.5-r4"}]}],"versions":["4.0.1-r0","4.0.1-r1","4.0.1-r2","4.0.1-r3","4.1.0-r0","4.1.0-r1","4.1.0-r2","4.1.1-r0","4.1.1-r1","4.1.1-r2","4.1.2-r10","4.1.2-r11","4.1.2-r12","4.1.2-r3","4.1.2-r4","4.1.2-r5","4.1.2-r6","4.1.2-r7","4.1.2-r8","4.1.2-r9","4.1.3-r0","4.10.0-r0","4.10.0-r1","4.10.0-r2","4.10.0-r3","4.10.1-r0","4.10.1-r1","4.10.1-r2","4.11.0-r0","4.11.0-r1","4.11.1-r0","4.11.1-r1","4.12.0-r0","4.12.0-r1","4.12.0-r2","4.12.0-r3","4.12.1-r0","4.12.1-r1","4.12.1-r2","4.13.0-r0","4.13.0-r1","4.13.0-r2","4.13.0-r3","4.13.0-r4","4.13.1-r0","4.13.1-r1","4.13.1-r2","4.13.1-r3","4.13.1-r4","4.13.1-r5","4.14.0-r0","4.14.0-r1","4.14.0-r2","4.14.0-r3","4.14.1-r0","4.14.1-r1","4.14.1-r2","4.14.1-r3","4.14.1-r4","4.14.1-r5","4.15.0-r0","4.15.0-r1","4.15.0-r2","4.15.0-r3","4.15.0-r4","4.15.0-r5","4.15.1-r0","4.15.1-r1","4.15.1-r2","4.15.1-r3","4.16.0-r0","4.16.0-r1","4.16.1-r0","4.16.1-r1","4.16.1-r2","4.16.1-r3","4.16.1-r4","4.16.1-r5","4.16.1-r6","4.16.1-r7","4.16.2-r0","4.16.2-r1","4.16.2-r2","4.16.2-r3","4.17.0-r0","4.17.0-r1","4.17.0-r2","4.17.0-r3","4.17.0-r4","4.17.0-r5","4.17.1-r0","4.17.1-r1","4.17.1-r2","4.17.1-r3","4.17.1-r4","4.17.1-r5","4.17.2-r0","4.17.2-r1","4.17.2-r2","4.17.2-r3","4.17.2-r4","4.18.0-r0","4.18.0-r1","4.18.0-r2","4.18.0-r3","4.18.0-r4","4.18.0-r5","4.18.2-r0","4.18.2-r1","4.18.3-r0","4.18.3-r1","4.18.3-r2","4.18.4-r0","4.18.4-r1","4.18.5-r0","4.18.5-r1","4.18.5-r2","4.18.5-r3","4.2.0-r0","4.2.0-r1","4.2.0-r2","4.2.0-r3","4.2.0-r4","4.2.0-r5","4.2.0-r6","4.2.0-r7","4.2.1-r0","4.2.1-r1","4.2.1-r10","4.2.1-r11","4.2.1-r2","4.2.1-r3","4.2.1-r4","4.2.1-r5","4.2.1-r6","4.2.1-r7","4.2.1-r8","4.2.1-r9","4.2.2-r0","4.2.2-r10","4.2.2-r11","4.2.2-r2","4.2.2-r3","4.2.2-r4","4.2.2-r5","4.2.2-r6","4.2.2-r7","4.2.2-r8","4.2.2-r9","4.3.0-r0","4.3.0-r1","4.3.0-r2","4.3.0-r3","4.3.0-r4","4.3.0-r5","4.3.0-r6","4.3.0-r7","4.3.0-r8","4.3.1-r0","4.3.1-r1","4.3.1-r2","4.3.1-r3","4.3.2-r0","4.3.2-r1","4.3.2-r2","4.3.2-r3","4.3.2-r4","4.3.3-r0","4.4.1-r0","4.4.1-r1","4.4.1-r2","4.4.1-r3","4.4.1-r4","4.4.1-r5","4.4.1-r6","4.4.1-r7","4.4.1-r8","4.4.2-r0","4.4.2-r1","4.5.0-r0","4.5.0-r1","4.5.1-r0","4.5.1-r1","4.5.1-r2","4.5.1-r3","4.6.0-r0","4.6.0-r1","4.6.0-r2","4.6.0-r3","4.6.0-r4","4.6.0-r5","4.6.1-r0","4.6.1-r1","4.6.1-r2","4.6.3-r0","4.6.3-r1","4.7.0-r0","4.7.0-r1","4.7.0-r2","4.7.0-r3","4.7.0-r4","4.7.0-r5","4.7.1-r0","4.7.1-r1","4.7.1-r2","4.7.1-r3","4.7.1-r4","4.7.1-r5","4.7.2-r0","4.8.1-r0","4.8.1-r1","4.8.1-r2","4.8.1-r3","4.8.1-r4","4.9.0-r0","4.9.0-r1","4.9.0-r2","4.9.0-r3","4.9.0-r4","4.9.0-r5","4.9.0-r6","4.9.0-r7","4.9.0-r8","4.9.1-r0","4.9.1-r1","4.9.1-r2","4.9.1-r3"],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/alpine/ALPINE-CVE-2026-23553.json"}},{"package":{"name":"xen","ecosystem":"Alpine:v3.21","purl":"pkg:apk/alpine/xen?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.19.4-r1"}]}],"versions":["4.0.1-r0","4.0.1-r1","4.0.1-r2","4.0.1-r3","4.1.0-r0","4.1.0-r1","4.1.0-r2","4.1.1-r0","4.1.1-r1","4.1.1-r2","4.1.2-r10","4.1.2-r11","4.1.2-r12","4.1.2-r3","4.1.2-r4","4.1.2-r5","4.1.2-r6","4.1.2-r7","4.1.2-r8","4.1.2-r9","4.1.3-r0","4.10.0-r0","4.10.0-r1","4.10.0-r2","4.10.0-r3","4.10.1-r0","4.10.1-r1","4.10.1-r2","4.11.0-r0","4.11.0-r1","4.11.1-r0","4.11.1-r1","4.12.0-r0","4.12.0-r1","4.12.0-r2","4.12.0-r3","4.12.1-r0","4.12.1-r1","4.12.1-r2","4.13.0-r0","4.13.0-r1","4.13.0-r2","4.13.0-r3","4.13.0-r4","4.13.1-r0","4.13.1-r1","4.13.1-r2","4.13.1-r3","4.13.1-r4","4.13.1-r5","4.14.0-r0","4.14.0-r1","4.14.0-r2","4.14.0-r3","4.14.1-r0","4.14.1-r1","4.14.1-r2","4.14.1-r3","4.14.1-r4","4.14.1-r5","4.15.0-r0","4.15.0-r1","4.15.0-r2","4.15.0-r3","4.15.0-r4","4.15.0-r5","4.15.1-r0","4.15.1-r1","4.15.1-r2","4.15.1-r3","4.16.0-r0","4.16.0-r1","4.16.1-r0","4.16.1-r1","4.16.1-r2","4.16.1-r3","4.16.1-r4","4.16.1-r5","4.16.1-r6","4.16.1-r7","4.16.2-r0","4.16.2-r1","4.16.2-r2","4.16.2-r3","4.17.0-r0","4.17.0-r1","4.17.0-r2","4.17.0-r3","4.17.0-r4","4.17.0-r5","4.17.1-r0","4.17.1-r1","4.17.1-r2","4.17.1-r3","4.17.1-r4","4.17.1-r5","4.17.2-r0","4.17.2-r1","4.17.2-r2","4.17.2-r3","4.17.2-r4","4.18.0-r0","4.18.0-r1","4.18.0-r2","4.18.0-r3","4.18.0-r4","4.18.0-r5","4.18.2-r0","4.18.2-r1","4.18.2-r2","4.19.0-r0","4.19.0-r1","4.19.1-r0","4.19.2-r0","4.19.2-r1","4.19.2-r2","4.19.3-r0","4.19.3-r1","4.19.3-r2","4.19.4-r0","4.2.0-r0","4.2.0-r1","4.2.0-r2","4.2.0-r3","4.2.0-r4","4.2.0-r5","4.2.0-r6","4.2.0-r7","4.2.1-r0","4.2.1-r1","4.2.1-r10","4.2.1-r11","4.2.1-r2","4.2.1-r3","4.2.1-r4","4.2.1-r5","4.2.1-r6","4.2.1-r7","4.2.1-r8","4.2.1-r9","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