SB2026080210 - Multiple vulnerabilities in Citrix XenServer
Published: August 2, 2026
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 7 vulnerabilities.
1) Improper Initialization (CVE-ID: CVE-2026-42492)
CWE-ID: CWE-665 - Improper Initialization
CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
The vulnerability allows a local user to cause a denial of service.
The vulnerability exists due to improper state management in the VIRQ_DOM_EXC virtual IRQ binding logic when binding event channels. A local user can trigger an error path from an unprivileged domain to cause a denial of service.
A hypervisor crash with host-wide impact is also possible, although unlikely.
2) Type Confusion (CVE-ID: CVE-2026-62428)
CWE-ID: CWE-843 - Type confusion
CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
The vulnerability allows a local user to escalate privileges.
The vulnerability exists due to type confusion in grant-copy operations when processing grant-copy requests involving a pinned grant. A local user can trigger concurrent grant operations to escalate privileges.
Information disclosure and denial of service are also possible. Systems built without grant table support are not vulnerable.
3) Division by zero (CVE-ID: CVE-2026-62431)
CWE-ID: CWE-369 - Divide By Zero
CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
The vulnerability allows a local user to cause a denial of service.
The vulnerability exists due to division by zero in the periodic Viridian STIMER handling logic when processing a user-controlled divisor value. A local user can set the divisor to zero to cause a denial of service.
Only HVM guests with Viridian STIMERs enabled can trigger the vulnerability.
4) Race condition (CVE-ID: CVE-2026-62432)
CWE-ID: CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
The vulnerability allows a local attacker to cause a denial of service.
The vulnerability exists due to a race condition in the EVTCHNOP_expand_array hypercall when checking whether FIFO event channels are enabled without holding the correct lock. A local attacker can trigger EVTCHNOP_expand_array to race with EVTCHNOP_reset to cause a denial of service.
The issue affects malicious guest contexts, including HVM guests on x86 or ARM and PVH guests; x86 PV guests may also be able to trigger memory corruption or privilege escalation.
5) Out-of-bounds write (CVE-ID: CVE-2026-62434)
CWE-ID: CWE-787 - Out-of-bounds write
CVSSv4: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
The vulnerability allows a local user to cause a denial of service.
The vulnerability exists due to memory corruption in Xen memory management state when reclaiming special pages in populate-on-demand guests. A local user can attempt to reclaim pages that are not regular guest ram to cause a denial of service.
Only x86 HVM and PVH guests started in populate-on-demand mode are believed to be able to leverage the vulnerability.
6) Race condition (CVE-ID: CVE-2026-62435)
CWE-ID: CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CVSSv4: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
The vulnerability allows a local user to escalate privileges.
The vulnerability exists due to a race condition in grant-table version switching logic when switching from grant table v1 to v2 while other grant-table operations are in progress. A local user can trigger concurrent grant-table operations in a multi-vCPU guest to escalate privileges.
Only x86 guests permitted to use grant table version 2 interfaces are vulnerable, and exploitation requires a multi-vCPU guest.
7) Race condition (CVE-ID: CVE-2026-62436)
CWE-ID: CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CVSSv4: CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
The vulnerability allows a local user to escalate privileges.
The vulnerability exists due to a race condition in grant-table version switching logic when switching from grant table v2 to v1 while other grant-table operations are in progress. A local user can trigger concurrent grant-table operations in a multi-vCPU guest to escalate privileges.
Only x86 guests permitted to use grant table version 2 interfaces are vulnerable, and exploitation requires a multi-vCPU guest.
Remediation
Install update from vendor's website.