MEDIUM CVSS 5.0
Published: 2026-07-01

CVE-2026-54786

bytecodealliance wasmtime Security Advisory (CVE-2026-54786)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-54786 impacting bytecodealliance wasmtime. Evaluated with CVSS Base Score of 5.0 (MEDIUM).

Original NVD Description

Source: NIST NVD
Wasmtime is a runtime for WebAssembly. All versions prior to 24.0.10; versions 25.0.0 through those before 36.0.11; versions 37.0.0 through those before 44.0.3; and versions 45.0.0 and 45.0.1 contain a native implementation of WASIp1 which suffers from a leak in the fd_renumber function where the file descriptor being renumbered to is not properly closed. Wasmtime's implementation erroneously only updated the table of descriptors for WASIp1 and didn't update the underlying table of descriptors used by the host. This behavior means that while fd_renumber works correctly from a guest's perspective it ends up leaking resources in the host that aren't cleaned up until the corresponding Store is destroyed. In a loop, guests can use fd_renumber to cause hosts to exhaust both resources and file descriptors. This bug only affects the native implementation of WASIp1, meaning that only runtimes which load core wasm modules and expose fd_renumber are affected. Runtimes are additionally only affected if they expose the ability to acquire a file descriptor, such as opening a file. For runtimes that deny access to files they are unaffected. This issue has been fixed in versions 24.0.10, 36.0.11, 44.0.3, and 45.0.2.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Network (AV:N)
Exploitable remotely across internet boundaries
Attack Complexity
Low (AC:L)
No specialized conditions required
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
None (C:N)
No data confidentiality impact
Integrity
None (I:N)
No system modification impact
Availability
Low (A:L)
Partial service performance degradation

🎯 Affected Versions Matrix

Affected Product bytecodealliance / wasmtime
Affected Versions *
Weakness Enumeration CWE-400

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-2026-54786 impacting bytecodealliance wasmtime.

⚡ Nuclei Detection Template (YAML) cve-2026-54786.yaml
id: cve-2026-54786

info:
  name: bytecodealliance wasmtime - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: medium
  description: |
    Automated signature & scanner for CVE-2026-54786 affecting bytecodealliance wasmtime.
    Evaluation: Wasmtime is a runtime for WebAssembly. All versions prior to 24.0.10; versions 25.0.0 through those before  36.0.11; versions 37.0.0 through those bef...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-54786
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:L
    cvss-score: 5.0
    cve-id: CVE-2026-54786
    cwe-id: CWE-400
  tags: cve,cve-2026-54786,bytecodealliance,wasmtime,medium

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-2026-54786.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-54786
# Target: bytecodealliance wasmtime | CVSS: 5.0 (MEDIUM)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-54786 (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-2026-54786.sh
# Recommended Remediation & Patching Commands for CVE-2026-54786
# 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.

🔗 Verified Technical References

Authorities
  • No records filed in this category.
Distributions
  • No records filed in this category.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2026-54786 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-2026-54786?

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-2026-54786?

CVE-2026-54786 is classified with a CVSS 3.1 Base Score of 5.0 (MEDIUM). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
5.0
MEDIUM SEVERITY
CVE ID CVE-2026-54786
Weakness CWE-400
Vendor bytecodealliance
Product wasmtime
Published 2026-07-01
Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:L