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CVE-2026-18549— @fastify/multipart vulnerable to Denial of Service via aborted upload after fileSize limit

Quick assessment

Affected
@fastify/multipart @fastify/multipart
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Fastify @fastify/multipart是Fastify组织的一个处理multipart表单数据上传的插件。 Fastify @fastify/multipart 5.3.0版本至10.1.1之前版本存在资源管理错误漏洞，该漏洞源于busboy文件大小限制截断文件部分时，插件清除内部当前文件引用但底层流仍打开，若客户端中止连接，清理过程无法找到流，导致saveRequestFiles()永不完成，请求处理程序挂起，临时文件无法清理。可能导致未经身份验证的攻击者重复操作，造成临时文件泄露和处理器

CVSS 7.5 · High EPSS 0.60% · P49

Affected Version Matrix 2

VendorProduct Version RangeStatus
@fastify/multipart @fastify/multipart 5.3.0< 10.1.1 affected
10.1.1 unaffected
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I. Basic Information for CVE-2026-18549

Vulnerability Information
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Vulnerability Title
@fastify/multipart vulnerable to Denial of Service via aborted upload after fileSize limit
Source: CVE Program / CVE List V5
Vulnerability Description
@fastify/multipart is a multipart form-data parser for Fastify. In versions from 5.3.0 up to but not including 10.1.1, when the busboy fileSize limit truncates a file part, the plugin clears its internal current-file reference while the underlying stream is still open. If the client then aborts the connection before sending the terminating boundary, the abort cleanup finds no stream to destroy, so saveRequestFiles() never settles, the request handler hangs, and the temporary file already written to disk is never cleaned up. An unauthenticated client can repeat this to permanently leak temporary files and suspended handler executions, leading to disk and event-loop exhaustion. The issue is fixed in @fastify/multipart 10.1.1. Users should upgrade to 10.1.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
Fastify @fastify/multipart 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Fastify @fastify/multipart是Fastify组织的一个处理multipart表单数据上传的插件。 Fastify @fastify/multipart 5.3.0版本至10.1.1之前版本存在资源管理错误漏洞，该漏洞源于busboy文件大小限制截断文件部分时，插件清除内部当前文件引用但底层流仍打开，若客户端中止连接，清理过程无法找到流，导致saveRequestFiles()永不完成，请求处理程序挂起，临时文件无法清理。可能导致未经身份验证的攻击者重复操作，造成临时文件泄露和处理器
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
@fastify/multipart @fastify/multipart 5.3.0 ~ 10.1.1 -

II. Public POCs for CVE-2026-18549

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 5487 chars
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III. Intelligence Information for CVE-2026-18549

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Vendor Advisories for CVE-2026-18549 (1)

IV. Related Vulnerabilities

Same product: @fastify/multipart
Same vendor: @fastify/multipart
Same weakness: CWE-400