CVE-2026-29649
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 · uneditedNEMU contains an implementation flaw in its RISC-V Hypervisor CSR handling where henvcfg[7:4] (CBIE/CBCFE/CBZE-related fields) is incorrectly masked/updated based on menvcfg[7:4], so a machine-mode write to menvcfg can implicitly modify the hypervisor's environment configuration. This can lead to incorrect enforcement of virtualization configuration and may cause unexpected traps or denial of service when executing cache-block management instructions in virtualized contexts (V=1).
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 confidenceNEMU's RISC-V Hypervisor CSR handling incorrectly updates henvcfg[7:4] (CBIE/CBCFE/CBZE cache-block management fields) based on menvcfg[7:4] values. When machine-mode writes to menvcfg, it implicitly and incorrectly modifies the hypervisor's environment configuration, breaking virtualization isolation for cache-block management instructions when V=1 and potentially causing unexpected traps or denial of service.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE dataall versionsCVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify if Xiangshan NEMU is in useCheck the NEMU version or binary name (e.g., nemu --version, or identify the binary as 'nemu' from Xiangshan)Affected if The system runs Xiangshan NEMU emulator for RISC-V
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Confirm hypervisor extension is enabledVerify the CPU configuration includes the 'H' (hypervisor) extension, typically shown in the ISA string (e.g., rv64gcvh)Affected if The hypervisor extension is present and virtual machine mode (V=1) can be used
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Read the menvcfg CSR valueFrom a RISC-V hart running in machine mode (M-mode), read CSR 0x310 (menvcfg) and note the bits at positions 7:4 (CBIE, CBCFE, CBZE fields)Affected if The system is running in M-mode and can read menvcfg
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Read the henvcfg CSR valueFrom the same hart, read CSR 0x610 (henvcfg) and compare bits 7:4 with menvcfg bits 7:4Affected if The hypervisor is implemented and henvcfg is readable
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Test for incorrect coupling between CSRsWrite a new value to menvcfg bits 7:4 from M-mode, then re-read henvcfg bits 7:4 to see if they changed unexpectedlyAffected if henvcfg[7:4] changes after writing to menvcfg[7:4], indicating the virtualization isolation bug is present
If the system runs Xiangshan NEMU with hypervisor mode enabled and henvcfg[7:4] incorrectly mirrors menvcfg[7:4] changes, the environment is affected by CVE-2026-29649.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor dataApply the vendor patch to fix the henvcfg/menvcfg masking logic in NEMU's RISC-V hypervisor CSR handling; validate that henvcfg values remain independent of menvcfg writes in virtualized environments.
- Consultation4.0 h
- Implementation8.0 h
- Testing12.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-29649 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-29649 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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