CVE-2026-5079
Multer vulnerable to Denial of Service via deeply nested field names
Description
### Impact Multer is vulnerable to a Denial of Service (DoS) via deeply nested field names in multipart form data. The `append-field` dependency parses bracket notation in field names (e.g., `a[b][c]`) 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 `2.2.0` and configure `limits.fieldNestingDepth` 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.
How to fix CVE-2026-5079
To remediate CVE-2026-5079, upgrade the affected package to a fixed version below.
- —upgrade to 2.2.0 or later
Is CVE-2026-5079 being exploited?
No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-5079.
Affected packages (1)
- >= 1.0.0, < 2.2.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |