CVE-2026-56764 Overview
CVE-2026-56764 is a timing attack vulnerability affecting the Hono web framework in versions prior to 4.11.10. The flaw resides in the basicAuth and bearerAuth middleware components, which rely on a timingSafeEqual function that does not perform constant-time string comparison. Attackers can measure response time differences to progressively infer valid credential characters. The issue is classified under CWE-208: Observable Timing Discrepancy.
Critical Impact
Remote attackers without authentication can exploit measurable timing differences in credential comparison to recover valid basic auth passwords or bearer tokens, leading to authentication bypass in applications built on vulnerable Hono versions.
Affected Products
- Hono web framework versions prior to 4.11.10
- Applications using the basicAuth middleware
- Applications using the bearerAuth middleware
Discovery Timeline
- 2026-07-15 - CVE-2026-56764 published to NVD
- 2026-07-15 - Last updated in NVD database
Technical Details for CVE-2026-56764
Vulnerability Analysis
Hono is a JavaScript web framework designed for edge runtimes such as Cloudflare Workers, Deno, and Bun. The framework ships with authentication middleware including basicAuth for HTTP Basic Authentication and bearerAuth for bearer token validation. Both middlewares depend on an internal timingSafeEqual helper to compare submitted credentials against expected values.
The helper does not enforce constant-time semantics. Instead, the underlying comparison exits early when the first mismatching byte is encountered. This behavior creates a measurable relationship between the number of matching leading characters and the time required to reject the request.
An attacker who can issue repeated authentication attempts and measure response latency can iteratively determine each byte of a secret. Given a sufficiently large sample of requests to average out network jitter, the credential space collapses from exponential to linear in the length of the secret.
Root Cause
The root cause is the use of non-constant-time string comparison inside the timingSafeEqual function used by basicAuth and bearerAuth. Rather than comparing every byte regardless of match state, the function terminates as soon as a mismatch is detected. This design violates the invariant required for cryptographic equality checks on secret material.
Attack Vector
Exploitation requires network access to an endpoint protected by the vulnerable middleware. The attacker submits a large volume of authentication requests, varying one byte position at a time, and records the response latency for each attempt. Statistical analysis of the collected timings reveals which candidate byte produced the longest processing time before rejection, indicating a correct prefix match. The process repeats for each byte until the full credential is recovered.
Successful exploitation requires precise timing measurements and typically favors low-latency network positions or high request volumes. Detailed technical background is available in the GitHub Security Advisory and the VulnCheck Timing Attack Advisory.
Detection Methods for CVE-2026-56764
Indicators of Compromise
- High volumes of failed authentication requests from a single source targeting basicAuth or bearerAuth protected routes.
- Sequential authentication attempts where submitted credentials differ by a single byte position between requests.
- Sustained request patterns with unusually uniform intervals designed to reduce timing noise.
Detection Strategies
- Inventory application dependencies to identify Hono versions prior to 4.11.10 in package manifests such as package.json and lockfiles.
- Instrument authentication middleware to log failed attempts with client identifiers and correlate bursts of near-identical credential submissions.
- Deploy rate limiting and alert on anomalies in the number of 401 responses per client over short time windows.
Monitoring Recommendations
- Forward authentication logs and web application firewall telemetry to a centralized analytics platform for correlation.
- Track distributions of request latency on authentication endpoints and alert on statistical probing patterns.
- Monitor outbound egress from edge functions for any signs of credential misuse following suspected probing activity.
How to Mitigate CVE-2026-56764
Immediate Actions Required
- Upgrade Hono to version 4.11.10 or later across all deployments using basicAuth or bearerAuth.
- Audit source code and lockfiles for direct or transitive dependencies on vulnerable Hono releases.
- Rotate any credentials or bearer tokens that were validated by vulnerable middleware in production.
Patch Information
The maintainers addressed the issue in Hono 4.11.10 by replacing the flawed comparison with a constant-time implementation. Fix details and remediation guidance are documented in the GitHub Security Advisory GHSA-gq3j-xvxp-8hrf.
Workarounds
- Replace calls to the built-in middleware with a custom handler that uses crypto.timingSafeEqual from a trusted runtime library.
- Enforce strict rate limiting on authentication endpoints to raise the cost of statistical timing analysis.
- Place vulnerable services behind a reverse proxy or gateway that adds randomized response delays to authentication failures until patching is complete.
# Configuration example
npm install hono@^4.11.10
npm ls hono
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
