Goal Reached Thanks to every supporter — we hit 100%!

Goal: 1000 CNY · Raised: 1359 CNY

100%
Buy Us a Coffee

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.

expressjs Multer是expressjs组织开源的一个用于Node.js中间件。 expressjs Multer 2.3.0之前版本存在竞争条件问题漏洞，该漏洞源于使用异步fileFilter与fileSize限制时文件流处理存在竞争条件，可能导致超过配置大小限制的文件绕过大小限制拒绝。

CVSS 3.7 · Low EPSS 0.23% · P13

Possible ATT&CK Techniques 1 AI

T1059.007 · JavaScript

Affected Version Matrix 2

VendorProduct Version RangeStatus
multer multer < 2.3.0 affected
2.3.0 unaffected
Get alerts for future matching vulnerabilities Log in to subscribe

I. Basic Information for CVE-2026-77063

Vulnerability Information
Have questions about the vulnerability? See if Shenlong's analysis helps!
View Shenlong Deep Dive ↗

Although we use advanced large model technology, its output may still contain inaccurate or outdated information.Shenlong tries to ensure data accuracy, but please verify and judge based on the actual situation.

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
Vulnerability Title
expressjs Multer 竞争条件问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
expressjs Multer是expressjs组织开源的一个用于Node.js中间件。 expressjs Multer 2.3.0之前版本存在竞争条件问题漏洞，该漏洞源于使用异步fileFilter与fileSize限制时文件流处理存在竞争条件，可能导致超过配置大小限制的文件绕过大小限制拒绝。
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
multer multer 0 ~ 2.3.0 -

II. Public POCs for CVE-2026-77063

# POC Description Source Link Shenlong Link
AI-Generated POC Premium

No public POC found.

Login to generate AI POC

III. Intelligence Information for CVE-2026-77063

请登录查看更多情报信息。

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

No comments yet

Leave a comment