CVE-2026-79609
Description
A flaw was found in Xen. A malicious paravirtualized (PV) guest can cause a denial of service (DoS) by crashing the host hypervisor. During Xen Page Table Isolation (XPTI) processing, Xen attempts to access guest root page tables located in memory beyond the direct memory mapping boundary. Attempting to read this unmapped memory causes the hypervisor to fail, rendering the physical host and all hosted virtual machines unavailable.
Statement
XPTI copies 64-bit PV guest page table entries via the directmap, which may not cover memory beyond the 5 TiB (CONFIG_BIGMEM=y: 3.5 TiB) boundary; only x86 hosts running 64-bit PV guests with RAM above that boundary are affected; HVM/PVH guests and Arm are not affected.
Mitigation
avoid running 64-bit PV guests, or limit hypervisor memory via the command line mem=5T (CONFIG_BIGMEM=n) or mem=3584G (CONFIG_BIGMEM=y).
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
An attacker could get secret values such as cryptographic keys, PII, memory addresses, or other information that could be used in additional attacks.
Confidentiality
Technical Impact: Bypass Protection Mechanism
Out-of-bounds memory could contain memory addresses or other information that can be used to bypass ASLR and other protection mechanisms in order to improve the reliability of exploiting a separate weakness for code execution.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
An attacker could cause a segmentation fault or crash by causing memory to be read outside of the bounds of the buffer. This is especially likely when the code reads a variable amount of data and assumes that a sentinel exists to stop the read operation, such as a NUL in a string.
Other
Technical Impact: Varies by Context
The read operation could produce other undefined or unexpected results.
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