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PatchSiren cyber security CVE debrief

CVE-2026-5079 multer CVE debrief

CVE-2026-5079 is a HIGH severity vulnerability in multer, a popular Node.js middleware for handling multipart/form-data. The vulnerability allows an attacker to cause a Denial of Service (DoS) by sending a single HTTP request with a crafted multipart body containing deeply nested field names. This causes the append-field dependency to allocate deeply nested object structures, consuming excessive CPU and memory.

Vendor
multer
Product
Unknown
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-15
Original CVE updated
2026-06-16
Advisory published
2026-06-15
Advisory updated
2026-06-16

Who should care

Developers and administrators using multer versions 1.0.0 through 2.1.1 and 3.0.0-alpha.1 should be aware of this vulnerability and take immediate action to mitigate it.

Technical summary

The vulnerability is caused by the append-field dependency's lack of limit on nesting depth when parsing bracket notation in field names. This allows an attacker to force allocation of deeply nested object structures that consume CPU and memory.

Defensive priority

HIGH

Recommended defensive actions

  • 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 your application requires.
  • 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.

Evidence notes

The CVE record and NVD detail pages provide official information about this vulnerability.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-5079 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-5079

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-5079 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-5079

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Source reference

    Unverified legacy reference

    URL: https://cna.openjsf.org/security-advisories.html

    ce714d77-add3-4f53-aff5-83d477b104bb

  • Source reference

    Unverified legacy reference

    URL: https://github.com/expressjs/multer/security/advisories/GHSA-72gw-mp4g-v24j

    ce714d77-add3-4f53-aff5-83d477b104bb

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.