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Xen CVE-2026-23557

| EUVDEUVD-2026-30925 MEDIUM
Reachable Assertion (CWE-617)
2026-05-08 GHSA-9879-vj7m-r497
Buffer Overflow Linux Microsoft Xen
6.5
CVSS 3.1 · NVD
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Severity by source

NVD PRIMARY
6.5 MEDIUM
AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
vuln.today AI
6.5 MEDIUM

Guest-to-XenStore access requires local VM foothold with low privilege; no confidentiality or integrity impact, only host-level availability via scope change.

3.1 AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
4.0 AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
SUSE
MEDIUM
qualitative

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

3
Analysis Generated
Jul 23, 2026 - 22:56 vuln.today
CVE Published
May 08, 2026 - 06:45 oss-security
MEDIUM 6.5
CVE Published
May 08, 2026 - 06:45 nvd
UNKNOWN (no severity yet)

Description PRE-NVD

Disclosed via oss-security. NVD scoring and full description are pending.

AnalysisAI

Xenstored denial of service in Xen hypervisor (XSA-484) allows a low-privileged guest domain to crash the xenstored daemon by issuing a crafted XS_RESET_WATCHES command that triggers a reachable assertion (CWE-617), aborting the process. Because xenstored is the host-side service that brokers all inter-domain communication via XenStore, its crash disrupts all VMs co-resident on the host, explaining the Changed scope in the CVSS vector. No public exploit is identified at time of analysis and EPSS is 0.01% (2nd percentile), though the low exploitation complexity and high host-availability impact make this a meaningful risk in multi-tenant Xen deployments.

Technical ContextAI

Xenstored is the userspace daemon (or the C-library embedded variant oxenstored in OCaml) that implements the XenStore protocol - a lightweight key-value store used by Xen guests (domUs) and the privileged Domain 0 to exchange configuration data and device information. The XS_RESET_WATCHES command is a legitimate XenStore protocol operation used by guests to clear watch registrations. CWE-617 (Reachable Assertion) identifies the root cause: a defensive assertion inside the command handler is reachable via a guest-supplied command, causing the process to call abort() on assertion failure rather than returning an error. CPE cpe:2.3:o:xen:xen:*:*:*:*:*:*:*:* covers all Xen versions as potentially affected. The tags reference Linux and SUSE, consistent with xenstored running in a Linux Dom0 environment, and SUSE has issued multiple security updates (SUSE-SU-2026:1645, 1657, 1692, 1743, and 1998).

RemediationAI

Apply the vendor-released patch per XSA-484; the Xen Project advisory at https://xenbits.xenproject.org/xsa/advisory-484.html provides patch files for affected Xen trees. SUSE users should apply the relevant SUSE-SU-2026 updates (1645, 1657, 1692, 1743, or 1998) matching their SLES version from https://www.suse.com/support/update/. An exact patched Xen upstream release version is not independently confirmed from available data - consult the XSA-484 advisory for the specific patch branch and commit. As a compensating control where patching is not immediately possible, restricting guest access to the XS_RESET_WATCHES command via xenstore access control lists (if supported in the deployment) or isolating untrusted guests to dedicated Xen hosts reduces blast radius; however, these controls may disrupt legitimate guest watch-registration workflows and should be tested before deployment.

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Same weakness CWE-617 – Reachable Assertion

View all
CVE-2025-15684 MEDIUM POC
5.5
CVE-2016-8864 HIGH
7.5
CVE-2020-12417 HIGH POC
8.8
CVE-2020-6623 HIGH POC
8.8
CVE-2020-6619 HIGH POC
8.8
CVE-2020-6617 HIGH POC
8.8
CVE-2023-37023 HIGH POC
8.6
CVE-2023-37021 HIGH POC
8.6

Same technique Buffer Overflow

View all
CVE-2017-7269 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2015-3113 CRITICAL POC
9.8
CVE-2011-2462 CRITICAL POC
9.8
CVE-2020-0796 CRITICAL POC
10.0
CVE-2019-11043 CRITICAL POC
9.8
CVE-2009-0927 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8

Vendor StatusVendor

SUSE

Severity: Medium
Product Status
Image SLES15-SP4-BYOS-Azure Image SLES15-SP4-BYOS-GCE Image SLES15-SP4-CHOST-BYOS-Aliyun Image SLES15-SP4-CHOST-BYOS-Azure Image SLES15-SP4-CHOST-BYOS-GCE Image SLES15-SP4-CHOST-BYOS-SAP-CCloud Image SLES15-SP4-HPC-BYOS Image SLES15-SP4-HPC-BYOS-Azure Image SLES15-SP4-HPC-BYOS-GCE Image SLES15-SP4-HPC-GCE Image SLES15-SP4-Hardened-BYOS-Azure Image SLES15-SP4-Hardened-BYOS-GCE Image SLES15-SP4-SAP-Azure Image SLES15-SP4-SAP-BYOS-Azure Image SLES15-SP4-SAP-BYOS-GCE Image SLES15-SP4-SAP-GCE Image SLES15-SP4-SAP-Hardened Image SLES15-SP4-SAP-Hardened-Azure Image SLES15-SP4-SAP-Hardened-BYOS Image SLES15-SP4-SAP-Hardened-BYOS-Azure Image SLES15-SP4-SAP-Hardened-BYOS-GCE Image SLES15-SP4-SAP-Hardened-GCE Image SLES15-SP4-SAPCAL-Azure Image SLES15-SP4-SAPCAL-GCE Affected
Image SLES15-SP4-BYOS Image SLES15-SP4-BYOS-EC2 Image SLES15-SP4-CHOST-BYOS Image SLES15-SP4-CHOST-BYOS-EC2 Image SLES15-SP4-HPC-BYOS-EC2 Image SLES15-SP4-HPC-EC2 Image SLES15-SP4-Hardened-BYOS Image SLES15-SP4-Hardened-BYOS-EC2 Image SLES15-SP4-SAP Image SLES15-SP4-SAP-BYOS Image SLES15-SP4-SAP-BYOS-EC2 Image SLES15-SP4-SAP-EC2 Image SLES15-SP4-SAP-Hardened-BYOS-EC2 Image SLES15-SP4-SAPCAL Image SLES15-SP4-SAPCAL-EC2 Affected
Image SLES15-SP5-BYOS-Azure Image SLES15-SP5-BYOS-GCE Image SLES15-SP5-CHOST-BYOS-Aliyun Image SLES15-SP5-CHOST-BYOS-Azure Image SLES15-SP5-CHOST-BYOS-GCE Image SLES15-SP5-CHOST-BYOS-GDC Image SLES15-SP5-CHOST-BYOS-SAP-CCloud Image SLES15-SP5-GCE Image SLES15-SP5-HPC-BYOS-Azure Image SLES15-SP5-HPC-BYOS-GCE Image SLES15-SP5-Hardened-BYOS-Azure Image SLES15-SP5-Hardened-BYOS-GCE Image SLES15-SP5-SAP-Azure-3P Image SLES15-SP5-SAP-BYOS-Azure Image SLES15-SP5-SAP-BYOS-GCE Image SLES15-SP5-SAP-Hardened-Azure Image SLES15-SP5-SAP-Hardened-BYOS-Azure Image SLES15-SP5-SAP-Hardened-BYOS-GCE Image SLES15-SP5-SAP-Hardened-GCE Image SLES15-SP5-SAPCAL-Azure Image SLES15-SP5-SAPCAL-GCE Affected
Image SLES15-SP5-BYOS-EC2 Image SLES15-SP5-CHOST-BYOS-EC2 Image SLES15-SP5-EC2 Image SLES15-SP5-HPC-BYOS-EC2 Image SLES15-SP5-Hardened-BYOS-EC2 Image SLES15-SP5-SAP-BYOS-EC2 Image SLES15-SP5-SAP-Hardened-BYOS-EC2 Image SLES15-SP5-SAPCAL-EC2 Affected
Image SLES15-SP7-Azure-3P Image SLES15-SP7-Azure-Basic Image SLES15-SP7-Azure-Standard Image SLES15-SP7-BYOS-Azure Image SLES15-SP7-BYOS-GCE Image SLES15-SP7-CHOST-BYOS-Aliyun Image SLES15-SP7-CHOST-BYOS-Azure Image SLES15-SP7-CHOST-BYOS-GCE Image SLES15-SP7-CHOST-BYOS-GDC Image SLES15-SP7-CHOST-BYOS-SAP-CCloud Image SLES15-SP7-GCE Image SLES15-SP7-GCE-3P Image SLES15-SP7-HPC-BYOS-Azure Image SLES15-SP7-HPC-BYOS-GCE Image SLES15-SP7-Hardened-BYOS-Azure Image SLES15-SP7-Hardened-BYOS-GCE Image SLES15-SP7-SAP-Azure Image SLES15-SP7-SAP-Azure-3P Image SLES15-SP7-SAP-BYOS-Azure Image SLES15-SP7-SAP-BYOS-GCE Image SLES15-SP7-SAP-GCE Image SLES15-SP7-SAP-GCE-3P Image SLES15-SP7-SAP-Hardened-Azure Image SLES15-SP7-SAP-Hardened-BYOS-Azure Image SLES15-SP7-SAP-Hardened-BYOS-GCE Image SLES15-SP7-SAP-Hardened-GCE Image SLES15-SP7-SAPCAL-Azure Image SLES15-SP7-SAPCAL-GCE Affected

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CVE-2026-23557 vulnerability details – vuln.today
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