CVE-2026-69207
MediumCVSS 5.3Exploitation Probability (EPSS)
Low risk48th percentile - higher than 48% of all known CVEs
Summary
Hono before version 4.12.34 has a ReDoS vulnerability in the built-in CORS middleware (hono/cors). During a preflight OPTIONS request, the middleware parses the Access-Control-Request-Headers header using a regular expression with quadratic complexity, which can cause long CPU consumption and block request processing. This affects the default configuration when allowHeaders is unset or empty.
Risk Assessment
The risk includes potential service unavailability due to a single preflight request with a long run of whitespace, especially in runtimes sharing a single execution thread across requests.
Recommendation
Upgrade to version 4.12.34 or later. If upgrade is not possible, set a non-empty allowHeaders in the CORS configuration.
Original NVD description (English source)
Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.34, the built-in CORS middleware, hono/cors, is vulnerable to a regular expression denial of service (ReDoS). During a preflight OPTIONS request, the middleware parses the attacker-controlled Access-Control-Request-Headers header using a whitespace-tolerant regular expression whose backtracking makes its running time quadratic in the input length. Because the header value is bounded only by the deployment's maximum HTTP header size, a single preflight carrying a long run of whitespace can consume seconds of CPU and block request processing. On runtimes that share one execution thread across requests, this stalls concurrent requests as well, and repeated requests can render the service unresponsive. This affects the default configuration, since the vulnerable path is reached whenever cors() is used with an unset or empty allowHeaders. Applications that set a non-empty allowHeaders are not affected. This issue is fixed in version 4.12.34.