CVE-2026-5079: expressjs multer Uncontrolled Resource Consumption

Vulnerability summary

CVE-2026-5079 is a high (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in expressjs multer. EPSS estimates a 0.49% chance of exploitation in the next 30 days, higher than 40.7% of scored vulnerabilities.

Timeline

1. 15-06-2026
   PublishedVulnerability first disclosed.
2. 15-06-2026
   Last modifiedVulnerability information updated.

Description

Impact: multer versions 1.0.0 through 2.1.1 and 3.0.0-alpha.1 are vulnerable to a Denial of Service via deeply nested field names in multipart form data. The append-field dependency parses bracket notation in field names with no limit on nesting depth, allowing an attacker to force allocation of deeply nested object structures that consume CPU and memory. A single HTTP request with a crafted multipart body is sufficient to exploit this. Patches: Users should upgrade to multer 2.2.0 (2.x line) or 3.0.0-alpha.2 (3.x prerelease) and configure the new limits.fieldNestingDepth option to the minimum depth their application requires. Workarounds: Set limits.fields to a reasonable value to reduce the number of fields an attacker can send per request. This does not fully mitigate the issue but limits the impact.

• CWE-400Uncontrolled Resource ConsumptionThe product does not properly control the allocation and maintenance of a limited resource.