Bug 2458150 (CVE-2026-3842)

Summary: CVE-2026-3842 qemu-kvm: hyperv/syndbg: missing mapped-length guard after cpu_physical_memory_map causes host OOB write
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in QEMU. This vulnerability allows a local attacker within a guest virtual machine to write data beyond its allocated memory. This occurs when cpu_physical_memory_map() returns a shorter length than expected, leading to an out-of-bounds write. Successful exploitation could result in unauthorized access to guest memory or corruption of heap-allocated objects, potentially causing information disclosure, data integrity issues, or a denial of service.
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Bug Depends On: 2458151    
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Description OSIDB Bzimport 2026-04-14 07:34:16 UTC 
If cpu_physical_memory_map() returns a length shorter than the one that was passed into the function, writing the full out_len bytes causes an access beyond the memory allocated to the guest; or in the case of the MMIO bounce buffer, an out-of-bounds access in a heap-allocated object.

Upstream fix:
https://gitlab.com/qemu-project/qemu/-/commit/4f28b87fdd24df2049626106b7c24d0180952115