HIGH CVSS 7.8
Published: 2026-04-09

CVE-2026-34971

bytecodealliance wasmtime Security Advisory (CVE-2026-34971)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-34971 impacting bytecodealliance wasmtime. Evaluated with CVSS Base Score of 7.8 (HIGH).

Original NVD Description

Source: NIST NVD
Wasmtime is a runtime for WebAssembly. From 32.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Cranelift compilation backend contains a bug on aarch64 when performing a certain shape of heap accesses which means that the wrong address is accessed. When combined with explicit bounds checks a guest WebAssembly module this can create a situation where there are two diverging computations for the same address: one for the address to bounds-check and one for the address to load. This difference in address being operated on means that a guest module can pass a bounds check but then load a different address. Combined together this enables an arbitrary read/write primitive for guest WebAssembly when accesssing host memory. This is a sandbox escape as guests are able to read/write arbitrary host memory. This vulnerability has a few ingredients, all of which must be met, for this situation to occur and bypass the sandbox restrictions. This miscompiled shape of load only occurs on 64-bit WebAssembly linear memories, or when Config::wasm_memory64 is enabled. 32-bit WebAssembly is not affected. Spectre mitigations or signals-based-traps must be disabled. When spectre mitigations are enabled then the offending shape of load is not generated. When signals-based-traps are disabled then spectre mitigations are also automatically disabled. The specific bug in Cranelift is a miscompile of a load of the shape load(iadd(base, ishl(index, amt))) where amt is a constant. The amt value is masked incorrectly to test if it's a certain value, and this incorrect mask means that Cranelift can pattern-match this lowering rule during instruction selection erroneously, diverging from WebAssembly's and Cranelift's semantics. This incorrect lowering would, for example, load an address much further away than intended as the correct address's computation would have wrapped around to a smaller value insetad. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Local (AV:L)
Requires local system execution permissions
Attack Complexity
High (AC:H)
Depends on race conditions or environment
Privileges Required
Low (PR:L)
Standard user access required
User Interaction
None (UI:N)
Zero human interaction required
Scope
Changed (S:C)
Impacts components beyond caller authority
Confidentiality
High (C:H)
Total information disclosure
Integrity
High (I:H)
Total modification of target system
Availability
High (A:H)
Total denial of service or shutdown

🎯 Affected Versions Matrix

Affected Product bytecodealliance / wasmtime
Affected Versions *
Weakness Enumeration CWE-125

Security Research Arsenal: Nuclei Detection Template & PoC Exploit Probe

High-Intent Research Tool

Ready-to-use security scanner signatures, active verification probe skeletons, and remediation playbooks for CVE-2026-34971 impacting bytecodealliance wasmtime.

⚡ Nuclei Detection Template (YAML) cve-2026-34971.yaml
id: cve-2026-34971

info:
  name: bytecodealliance wasmtime - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: high
  description: |
    Automated signature & scanner for CVE-2026-34971 affecting bytecodealliance wasmtime.
    Evaluation: Wasmtime is a runtime for WebAssembly. From 32.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Cranelift compilation backend contains a bug ...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-34971
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
    cvss-score: 7.8
    cve-id: CVE-2026-34971
    cwe-id: CWE-125
  tags: cve,cve-2026-34971,bytecodealliance,wasmtime,high

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "wasmtime"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-34971.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-34971
# Target: bytecodealliance wasmtime | CVSS: 7.8 (HIGH)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-34971 (bytecodealliance wasmtime)...")
    headers = {
        "User-Agent": "CyberVault-Audit-Scanner/2.0",
        "Accept": "*/*"
    }
    try:
        r = requests.get(f"{target_url.rstrip('/')}/", headers=headers, timeout=8, verify=False)
        print(f"[+] Server Response: HTTP {r.status_code} | Server Banner: {r.headers.get('Server', 'Unknown')}")
        if r.status_code < 500:
            print(f"[!] Target reachable. Verify version against bytecodealliance wasmtime scope (*).")
        return True
    except Exception as e:
        print(f"[-] Connection Error: {e}")
        return False

if __name__ == '__main__':
    url = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8080"
    verify_vulnerability(url)
🛡️ Quick Patch & Remediation Script (Bash) patch_cve-2026-34971.sh
# Recommended Remediation & Patching Commands for CVE-2026-34971
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install wasmtime 2>/dev/null || \
sudo dnf upgrade wasmtime 2>/dev/null || \
sudo yum update wasmtime

# 2. Inspect installed package versions for vulnerable scope:
dpkg -l | grep -i wasmtime 2>/dev/null || rpm -qa | grep -i wasmtime

# 3. Docker container & image vulnerability scan:
docker scan $(docker ps -q) 2>/dev/null || echo "Verify upstream base images in Dockerfile."

🛡️ Remediation & Security Action

  • Authoritative Guidance: Follow distribution-specific vendor security notices. Advisory status and package patches vary by distribution release.
  • Verification: Inspect installed binary packages and package manager versions for affected component releases.
  • Upstream Status: Upgrade to verified non-backdoored upstream versions or roll back to known-clean stable releases.
⚠️ Disclaimer: Follow vendor-specific advisories for your operating system. CyberVault does not fabricate unsupported remediation scripts.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2026-34971 in bytecodealliance wasmtime?

Review vendor-specific security notices and update bytecodealliance wasmtime packages to the latest patched release immediately. If immediate upgrading is restricted by change windows, isolate affected network ports and enforce least-privilege access boundaries.

Is there an active exploit or public PoC for CVE-2026-34971?

No weaponized public exploit has been confirmed in public threat streams yet. Continuous surveillance is active across GitHub and security feeds.

What is the CVSS 3.1 severity rating and impact for CVE-2026-34971?

CVE-2026-34971 is classified with a CVSS 3.1 Base Score of 7.8 (HIGH). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
7.8
HIGH SEVERITY
CVE ID CVE-2026-34971
Weakness CWE-125
Vendor bytecodealliance
Product wasmtime
Published 2026-04-09
Vector CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H