CVE-2026-29645

Xiangshan Nemu 2025.12

Published

20 April 2026

Modified

24 April 2026

Patch / advisory

View advisory

CVSS Score v3.1 7.5

Click a component to see what it means

Raw vector

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

EPSS Score 0.0054 43th percentile

Risk Priority 58 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-29645 is a high-severity Incorrect Calculation of Buffer Size (CWE-131) vulnerability in Xiangshan Nemu. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 43th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-29645 is an improper instruction-validation vulnerability in the RISC-V Vector (RVV) decoder of NEMU, an open-source RISC-V emulator maintained under the OpenXiangShan/NEMU project. Specifically, versions of NEMU before v2025.12.r2 fail to correctly validate the funct3 field during decoding of vsetvli, vsetivli, and vsetvl instructions. This allows certain invalid OP-V instruction encodings to be misinterpreted and executed as vset* configuration instructions instead of triggering an illegal-instruction exception.

The vulnerability can be exploited by remote attackers with no privileges or user interaction required, as indicated by its CVSS 3.1 score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). An attacker can provide crafted RISC-V binaries to a system running the affected NEMU version, leading to incorrect trap behavior, architectural state corruption or divergence, and potential denial of service. Exploitation is feasible in environments relying on NEMU for accurate instruction emulation, such as testing, simulation, or sandboxing setups.

Mitigation is available through a patch in NEMU v2025.12.r2 and later versions. The fix is detailed in GitHub commit 481de637d5fc5838356caee80a79e56a33754039, which addresses the issue reported in OpenXiangShan/NEMU issue #952 and merged via pull request #958. Additional technical context on the affected RISC-V Vector instructions is provided in the RISC-V ISA unprivileged vector specification.

EU & UK References

🇪🇺 ENISA EUVD: EUVD-2026-23937

Vulnerability Data

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.

CWE(s): CWE-131 CWE-1287

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation

Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.

attack.mitre.org →

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1203 Exploitation for Client Execution Execution

Adversaries may exploit software vulnerabilities in client applications to execute code.

attack.mitre.org →

T1210 Exploitation of Remote Services Lateral Movement

Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.

attack.mitre.org →

T1212 Exploitation for Credential Access Credential Access

Adversaries may exploit software vulnerabilities in an attempt to collect credentials.

attack.mitre.org →

Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-29649Same product: Xiangshan Nemu

CVE-2023-3917Shared CWE-1287

CVE-2024-35213Shared CWE-1287

CVE-2025-12689Shared CWE-1287

CVE-2026-0280Shared CWE-131

CVE-2024-9404Shared CWE-1287

CVE-2024-51550Shared CWE-1287

CVE-2026-9742Shared CWE-1287

CVE-2023-3906Shared CWE-1287

CVE-2024-2105Shared CWE-1287

Affected Assets

xiangshan

nemu

2025.12

Mitigating Controls

Control response

Prevent

Stop it (NIST 800-53)

—

Detect

Catch it (NIST detect / respond)

—

Harden

Shrink the surface (DISA STIG)

—

Validate

Prove the fix (OWASP ASVS)

V1.1.1
V1.4.2
V2.1.1
V2.2.2

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer security testing and code review can discover incorrect buffer-size computations before deployment.

SI-10 Information Input Validation good match

SI-10 directly requires validation of information inputs, which structurally prevents type-validation failures from being introduced or exploitable.

SA-8 Security and Privacy Engineering Principles partial match

Secure engineering principles directly require correct buffer-size arithmetic and bounds-checked allocation.

SI-16 Memory Protection partial match

Memory-protection mechanisms limit the exploitability of an overflow that results from an incorrect size calculation.

SI-2 Flaw Remediation partial match

Flaw-remediation processes that include vulnerability scanning or static analysis will surface buffer-size errors.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match

prevents

Secure SDLC practices directly prevent buffer-size miscalculations via coding standards, reviews, and testing, while fixing this single weakness only partially fulfills the broader control.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.28 Secure coding mostly match

degrades

Secure coding standards directly require correct buffer-size calculations.

A.8.29 Security testing in development and acceptance mostly match

finds

Security testing can detect buffer-size errors before release.

A.8.25 Secure development life cycle partial match

prevents

Secure development lifecycle mandates size-checking practices that reduce buffer-size miscalculations.

A.8.26 Application security requirements partial match

prevents

Application security requirements can specify buffer-size validation rules.