Resource exhaustion in Expressjs Multer
CVE-2026-5079
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.
Vulnerability class: DoS (Denial of Service)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.005 (39.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 40th percentile — 39.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002
Affected products
- Expressjs Multer — versions 3.0.0
- Multer — versions 1.0.0, 2.2.0, 3.0.0-alpha.1
Weakness classification (CWE)
References
- ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-5079?
- CVE-2026-5079 is a high-severity vulnerability in Expressjs Multer, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-06-15.
- How severe is CVE-2026-5079?
- High severity. CVSS v3 base score is 7.5 out of 10.