CVE-2026-77037: expressjs multer Uncontrolled Resource Consumption

Vulnerability summary

CVE-2026-77037 is a high (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in expressjs multer. EPSS estimates a 0.35% chance of exploitation in the next 30 days, higher than 26.8% of scored vulnerabilities.

Timeline

1. 28-08-2026
   PublishedVulnerability first disclosed.
2. 31-08-2026
   Last modifiedVulnerability information updated.

Description

multer is a middleware for handling multipart/form-data in Node.js. In version 2.2.0, when a disk-backed upload is aborted or truncated before the write stream finishes, multer's disk storage engine removes the visible file but does not close the underlying write file descriptor, leaving a deleted but still open descriptor. A remote attacker able to reach an upload route using the built-in disk storage can send repeated aborted or malformed multipart uploads, each one leaking a file descriptor and retaining disk blocks until the process exits, which can exhaust resources and cause a denial of service. The issue is fixed in multer 2.3.0, which closes the destination write stream on abnormal source termination and defers cleanup until the stream has closed. Upgrade to multer 2.3.0 to remediate.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.
• CWE-459Incomplete CleanupThe product does not properly "clean up" and remove temporary or supporting resources after they have been used.