CVE-2026-120215— @fastify/cors vulnerable to Denial of Service on a CORS preflight with the onSend hook

Quick assessment

Affected

@fastify/cors @fastify/cors

Exploitation

No confirmed in-the-wild exploitation; assess based on exposure

Recommended action

Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

是 Fastify Web 框架的 CORS 插件。在 8.2.0 至 11.3.x 版本中，若应用程序以非默认的钩子选项注册该插件，则在处理 CORS 预检请求时会导致服务崩溃。当收到携带和请求头的 OPTIONS 请求时，插件会在钩子内部调用，从而重新进入响应发送流程；此时尝试第二次写入响应头会触发未捕获的错误，若未安装进程级错误处理器，该错误将直接终止 Node.js 进程。未经认证的远程攻击者仅需发送一次预检请求即可触发此漏洞。由于漏洞利用依赖于非默认的配置，因此其影响仅限于服务可用性。该问

CVSS 3.7 · Low Updated Nov 02, 2026

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

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Vulnerability Information

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Vulnerability Title

@fastify/cors vulnerable to Denial of Service on a CORS preflight with the onSend hook

Source: CVE Program / CVE List V5

Vulnerability Description

@fastify/cors is the CORS plugin for the Fastify web framework. In versions 8.2.0 through 11.3.x, an application that registers the plugin with the non-default onSend hook option crashes on a CORS preflight. On an OPTIONS request that carries the Origin and Access-Control-Request-Method headers, the plugin calls reply.send from inside the onSend hook and re-enters the send pipeline, so a second write of the response headers throws an uncaught ERR_HTTP_HEADERS_SENT that can terminate the Node.js process when no process-level handler is installed. An unauthenticated remote client can trigger this with a single preflight request, so the impact is availability only, and exploitation requires the non-default onSend configuration. The issue is fixed in @fastify/cors 11.4.0, where onSend is no longer an accepted hook value and registration fails with a clear error instead of crashing at request time, and users should upgrade to 11.4.0 or later. As a workaround, use any other hook such as the default onRequest, or set preflight to false.

Source: CVE Program / CVE List V5

CVSS Information

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

Source: CVE Program / CVE List V5

Vulnerability Type

未捕获的异常

Source: CVE Program / CVE List V5

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
@fastify/cors	@fastify/cors	8.2.0 ~ 11.4.0	-

II. Public POCs for CVE-2026-120215

#	POC Description	Source Link	Shenlong Link

AI-Generated POC Premium

No public POC found.

III. Intelligence Information for CVE-2026-120215

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Vendor Advisories for CVE-2026-120215 (1)

CVE-2026-120215: @fastify/cors vulnerable to Denial of Service on a CORS preflight with the onSend hook

https://www.cve.org/CVERecord?id=CVE-2026-120215

IV. Related Vulnerabilities

Same weakness: CWE-248