2.9

CVE-2026-23553: x86: incomplete IBPB for vCPU isolation

Analyzed
AliasesALPINE-CVE-2026-23553UBUNTU-CVE-2026-23553DEBIAN-CVE-2026-23553
Published 28-01-2026Last modified 28-01-2026

Vulnerability summary

CVE-2026-23553 is a low (CVSS 2.9) Improper Initialization vulnerability in xen. EPSS estimates a 0.14% chance of exploitation in the next 30 days, higher than 3.7% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 2.9, local access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
2.9/10
010
Low · v3.1 (CVE.org)
EPSS score
0.14%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 9 · Related 8
MGASA-2026-0026OPENSUSE-SU-2026:10118-1SUSE-SU-2026:0303-1SUSE-SU-2026:0304-1SUSE-SU-2026:0306-1SUSE-SU-2026:0328-1

Timeline

  1. 28-01-2026
    PublishedVulnerability first disclosed.
  2. 28-01-2026
    Last modifiedVulnerability information updated.

Description

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. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. Consider: 1) vCPU runs on CPU A, running task 1. 2) vCPU moves to CPU B, idle gets scheduled on A. Xen skips IBPB. 3) On CPU B, guest kernel switches from task 1 to 2, issuing IBPB. 4) vCPU moves back to CPU A. Xen skips IBPB again. Now, task 2 is running on CPU A with task 1's training still in the BTB.

CVSS metrics

5 scores · 5 sources · 1 version

EPSS trend

Probability

0.14%

Chance of exploitation in the next 30 days

Percentile

4%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.15% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: local access, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Alpine1 product
  • xen≥ 4.6.0, < 4.18.5-r4 | ≥ 4.6.0, < 4.19.4-r1 | ≥ 4.6.0, < 4.20.2-r1 | ≥ 4.6.0, < 4.21.0-r2
Debian1 product
  • xen< 4.17.7-0+deb12u1 | < 4.20.2+37-g61ff35323e-0+deb13u1 | < 4.20.2+37-g61ff35323e-1
Ubuntu1 product
  • xenAll versions (No fix recorded)
Xen1 product
  • xen≥ 4.6.0 (No fix recorded)

4 vendors · 4 products

References

8 links