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Fencer Intel
high 7.5

CVE-2026-5079 json

multer vulnerable to Denial of Service via deeply nested field names

published 4mo ago modified 4mo ago also EUVD-2026-36726 , GHSA-72gw-mp4g-v24j

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 20%
public exploits
0
none known

Summary

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.

Patch / fix

  • npm multer 2.2.0, 3.0.0-alpha.2
  • multer multer 2.2.0, 3.0.0-alpha.2

Is CVE-2026-5079 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-5079 updated cvss 7.5

multer: Multer: Denial of Service via deeply nested field names in multipart form data

  • Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/vector-rhel9
    affected: workaround, no fix available
  • Red Hat Ansible Automation Platform 2.1 ansible-automation-platform/automation-portal 1788775748
    fixed: vendor fix RHSA-2026:65118
  • Red Hat Ansible Automation Platform 2.2 ansible-automation-platform/bootc-automation-portal-rhel9 1788943531
    fixed: vendor fix RHSA-2026:66003
  • Red Hat Developer Hub 1.9 rhdh/rhdh-hub-rhel9 1785972843
    fixed: vendor fix RHSA-2026:52768
  • Red Hat Developer Hub 1.10 rhdh/rhdh-hub-rhel9 1785411652, rhdh/red-hat-developer-hub-backstage-plugin-lightspeed-backend 1785332487, rhdh/red-hat-developer-hub-backstage-plugin-orchestrator-backend 1785332825
    fixed: vendor fix RHSA-2026:48126
  • Red Hat Developer Hub 1.9 rhdh/rhdh-rhel9-operator 1785972533, rhdh/rhdh-operator-bundle 1785976147 Red Hat Developer Hub 1.10 rhdh/rhdh-rhel9-operator 1785411290, rhdh/rhdh-operator-bundle 1785415596, rhdh/rhdh-must-gather-rhel9 1784202439, rhdh/rhdh-rag-content-rhel9 1785162496, rhdh/red-hat-developer-hub-backstage-plugin-lightspeed 1785333413, rhdh/red-hat-developer-hub-backstage-plugin-orchestrator 1785340831, +3 more
    not affected: vulnerable code not present
  • Red Hat Enterprise Linux 7 firefox Red Hat Enterprise Linux 8 thunderbird Red Hat Enterprise Linux 9 firefox, firefox-x11, thunderbird
    not affected: vulnerable code not in execute path
  • Red Hat Enterprise Linux 10 firefox, thunderbird, fido-device-onboard Red Hat Trusted Profile Analyzer rhtpa/rhtpa-trustification-service-rhel9
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
4mo ago

Exploit prediction

0.28% chance of exploitation in the next 30 days, higher than 20% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
npm multer
>=1.0.0, <2.2.0
>=3.0.0-alpha.1, <3.0.0-alpha.2
2.2.0
3.0.0-alpha.2

Affected products

  • multer multer

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of expressjs/multer published their own advisory on GitHub. Reviewed sources take precedence over it.