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CWE-267Weakness · CWE-267

CVE-2026-29646

CRITICAL · 9.8 CVSS v3.1 Published 2026-04-20
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In OpenXiangShan NEMU prior to 55295c4, when running with RVH (Hypervisor extension) enabled, a VS-mode guest write to the supervisor interrupt-enable CSR (sie) may be handled incorrectly and can influence machine-level interrupt enable state (mie). This breaks privilege/virtualization isolation and can lead to denial of service or privilege-boundary violation in environments relying on NEMU for correct interrupt virtualization.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

In OpenXiangShan NEMU with RVH (Hypervisor extension) enabled, a VS-mode guest's write to the supervisor interrupt-enable CSR (sie) is incorrectly handled and improperly modifies the machine-level interrupt enable state (mie), violating privilege isolation between VS and machine modes.

MitigationUpgrade NEMU to version containing commit 55295c4 which corrects the sie CSR handling to properly virtualize interrupt enable bits without affecting machine-level mie state.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check if NEMU is built with RVH (Hypervisor extension) support enabled
    Inspect NEMU build configuration or run 'grep -r "RHV\|rvh" config' in the build directory. Look for CONFIG_RVH or similar hypervisor enable flags in the NEMU build configuration files.
    Affected if CONFIG_RVH or hypervisor support is enabled in the NEMU build configuration
  2. Verify NEMU version or commit hash
    Run 'git log --oneline -1' in the NEMU source directory or check NEMU version output. Compare the commit hash to 55295c4.
    Affected if The installed NEMU version is older than the commit containing fix 55295c4 (i.e., the commit hash is earlier in history than 55295c4)
  3. Confirm hypervisor extension is active at runtime
    Run NEMU with a guest that uses VS (Virtual Supervisor) mode and verify that the hypervisor extension is enumerated. Check CPUID or device tree for hypervisor bit presence, or inspect NEMU runtime logs for RVH/hypervisor initialization messages.
    Affected if RVH/hypervisor extension is reported as available or enabled in the emulated system
  4. Test sie CSR behavior from VS-mode guest
    From a VS-mode guest OS, write to the sie CSR (Supervisor Interrupt Enable) and then read the mie CSR (Machine Interrupt Enable) to verify mie was not modified. Alternatively, compare the mie value before and after sie writes from VS-mode.
    Affected if Writing to sie from VS-mode guest incorrectly modifies the machine-level mie register, indicating the vulnerability is present
  5. Inspect NEMU source code for sie handling in VS-mode
    In the NEMU source, locate the CSR handling code for sie (likely in src/isa/riscv/insn/csrmod.c or similar). Check if sie writes route through to mie when in VS-mode with RVH enabled, by examining the write handler for sie CSR.
    Affected if The sie CSR write handler directly modifies mie when executed from VS-mode with RVH enabled (code analysis confirms the bug)

A user is affected if NEMU is built with RVH/hypervisor support enabled, runs an older version before commit 55295c4, and executes a VS-mode guest where sie CSR writes improperly alter machine-level mie state.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch github.com →
Interim mitigation

Upgrade NEMU to version containing commit 55295c4 which corrects the sie CSR handling to properly virtualize interrupt enable bits without affecting machine-level mie state.

Recommended fix Moderate confidence

Upgrade to commit 55295c4 or later in the OpenXiangShan NEMU repository

  1. 1. Identify current NEMU version by checking the git commit hash in your deployment
  2. 2. Clone or pull the latest OpenXiangShan NEMU repository: git clone https://github.com/OpenXiangShan/NEMU.git
  3. 3. Navigate to the NEMU directory: cd NEMU
  4. 4. Fetch the latest changes: git fetch origin
  5. 5. Check out the fixed commit 55295c4 or a later version: git checkout 55295c4 (or git checkout <latest_tag> for tagged releases)
  6. 6. Rebuild NEMU according to the build instructions in the repository README
  7. 7. Verify the fix is applied by confirming the commit 55295c4 is in the git history: git log --oneline | head -10
  8. 8. Test the build with RVH (Hypervisor extension) enabled to confirm proper interrupt virtualization behavior

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing8.0 h
  • Review / QA4.0 h
24.0 hours of engineering $4,160
Get the patch applied

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,656.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-29646 in production — separate from our analysis above.

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What this is

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  • Version or environment caveats, and links to real fixes
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