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CVE-2026-77063— multer vulnerable to file size limit bypass via async fileFilter race condition

Quick assessment

Affected
multer multer
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.

multer 是一个用于在 Node.js 中处理 multipart/form-data 的中间件。当应用程序将异步 fileFilter 与 fileSize 限制配合使用时，multer 在文件流处理中的竞态条件可能使超过已配置大小限制的文件绕过大小限制的拒绝机制。所有 2.3.0 之前的版本均受影响。该问题的影响有限，因为底层的 multipart 解析器仍会在大小限制处截断数据流，因此这属于对“大小限制拒绝”机制的绕过，而非不可控的资源消耗。该问题已在 multer 2.3.0 中修复。请升级到 mult

CVSS 3.7 · Low

Possible ATT&CK Techniques 1 AI

T1059.007 · JavaScript
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I. Basic Information for CVE-2026-77063

Vulnerability Information
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Vulnerability Title
multer vulnerable to file size limit bypass via async fileFilter race condition
Source: CVE Program / CVE List V5
Vulnerability Description
multer is a middleware for handling multipart/form-data in Node.js. When an application uses an asynchronous fileFilter together with the fileSize limit, a race condition in multer's file stream handling can allow a file that exceeds the configured size limit to bypass the size-limit rejection. All versions before 2.3.0 are affected. The impact is limited because the underlying multipart parser still truncates the stream at the size limit, so this is a bypass of the limit rejection rather than uncontrolled resource consumption. The issue is fixed in multer 2.3.0. Upgrade to multer 2.3.0 to remediate.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用共享资源的并发执行不恰当同步问题(竞争条件)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
multer multer 0 ~ 2.3.0 -

II. Public POCs for CVE-2026-77063

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III. Intelligence Information for CVE-2026-77063

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Vendor Advisories for CVE-2026-77063 (1)

Same Patch Batch · multer · 2026-08-28 · 4 CVEs total

CVE-2026-77078 7.5 HIGH multer vulnerable to Denial of Service via crafted multipart field names
CVE-2026-77037 7.5 HIGH multer vulnerable to Denial of Service via file descriptor leak on aborted uploads
CVE-2026-82333 7.5 HIGH multer vulnerable to Denial of Service via oversized array index in field names

IV. Related Vulnerabilities

Same product: multer
Same vendor: multer
Same weakness: CWE-362

V. Comments for CVE-2026-77063

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