NEMU (OpenXiangShan/NEMU) before v2025.12.r2 contains an improper instruction-validation flaw in its RISC-V Vector (RVV) decoder. The decoder does not correctly validate the funct3 field when decoding vsetvli/vsetivli/vsetvl, allowing certain invalid OP-V instruction encodings to be misinterpreted and executed as vset* configuration instructions rather than raising an illegal-instruction exception. This can be exploited by providing crafted RISC-V binaries to cause incorrect trap behavior, architectural state corruption/divergence, and potential denial of service in systems that rely on NEMU for correct execution or sandboxing.
CVE-2026-29645
Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-04-20. NVD baseline CVSS 7.5; sources differ by 0.0.
- High severity, but no confirmed exploitation yet
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 7.5
- EG Score
- 7.5(medium)
- EG Risk
- —
- EPSS
- 42.3%
- KEV
- Not listed
Published
April 20, 2026
Last Modified
April 24, 2026
Advisory Details (4)
Auto-updated Jun 9, 2026fix(vector): remove incorrect decode for some insts
Fix merged in OpenXiangShan/NEMU PR #958 on 2025-12-03 — awaiting tagged release
https://github.com/OpenXiangShan/NEMU/pull/958Incorrect decode mask for vsetvli/vsetivli/vsetvl · Issue #952 · OpenXiangShan/NEMU · GitHub
https://github.com/OpenXiangShan/NEMU/issues/952commit 481de637d5fc (OpenXiangShan/NEMU)
Fix landed in OpenXiangShan/NEMU commit 481de637d5fc — awaiting tagged release
https://github.com/OpenXiangShan/NEMU/commit/481de637d5fc5838356caee80a79e56a33754039Untitled :: RISC-V Ratified Specifications Library
https://docs.riscv.org/reference/isa/unpriv/v-st-ext.htmlWeakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 14× in last 7d / 47× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
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