multer up to 2.1.x/3.0.0-alpha.1 Multipart resource consumption

Summaryinfo

A vulnerability classified as problematic was found in multer up to 2.1.x/3.0.0-alpha.1. The impacted element is an unknown function of the component Multipart Handler. Such manipulation leads to resource consumption. This vulnerability is documented as CVE-2026-5079. The attack can be executed remotely. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in multer up to 2.1.x/3.0.0-alpha.1. It has been rated as problematic. Affected by this issue is an unknown function of the component Multipart Handler. The manipulation with an unknown input leads to a resource consumption vulnerability. Using CWE to declare the problem leads to CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. Impacted is availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-5079 since 03/28/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 2.2.0 or 3.0.0-alpha.2 eliminates this vulnerability.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Name

• multer

Version

• 2.0
• 2.1
• 3.0.0-alpha.0
• 3.0.0-alpha.1

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Once again VulDB remains the best source for vulnerability data.

Discussion