Hono: ReDoS in CORS middleware via Access-Control-Request-Headers
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.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-69207
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 7 Nov 2026, 17:46 UTC · Revision 1
Source evidence
Hono: ReDoS in CORS middleware via Access-Control-Request-Headers
core-osv · Original sourcePublished 7 Aug 2026, 20:51 UTC
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.
osv:CVE-2026-69207
Complete source record
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"url": "https://osv.dev/vulnerability/CVE-2026-69207",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Hono: ReDoS in CORS middleware via Access-Control-Request-Headers",
"summary": "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.",
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],
"modified": "2026-10-28T02:30:51.296601611Z",
"provider": "osv",
"references": [
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"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/69xxx/CVE-2026-69207.json",
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"https://nvd.nist.gov/vuln/detail/CVE-2026-69207",
"https://github.com/honojs/hono/commit/93fc250d8b4df58ea542cb945171de8013d5e6d5"
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}
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"evidence": "/id"
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"severity_evidence": "/severity/0/score"
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"source_id": "core-osv",
"document_id": 520015,
"published_at": "2026-08-07T20:51:04.3+00:00"
}