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Fencer Vulns
low 3.7

CVE-2026-77063 json

multer vulnerable to file size limit bypass via async fileFilter race condition

published 2026-08-28 2 mo ago modified 2026-09-08 2 mo ago also GHSA-qvfw-j98x-7q72 , EUVD-2026-67929

cvss
3.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 9%
public exploits
0
none known

Summary

multer is a middleware for handling multipart/form-data in Node.js. When an application uses an asynchronous fileFilter together with the fileSize limit, a race condition in multer's file stream handling can allow a file that exceeds the configured size limit to bypass the size-limit rejection. All versions before 2.3.0 are affected. The impact is limited because the underlying multipart parser still truncates the stream at the size limit, so this is a bypass of the limit rejection rather than uncontrolled resource consumption. The issue is fixed in multer 2.3.0. Upgrade to multer 2.3.0 to remediate.

Patch / fix

  • npm multer 2.3.0
  • multer multer 2.3.0
  • node-multer Debian 14 2.4.0+~cs3.2.0-1

debian advisories DEBIAN-CVE-2026-77063

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-2026-77063 updated cvss 3.7

multer: Multer: File size limit bypass via asynchronous file filter race condition

  • Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/vector-rhel9 Red Hat 3scale API Management Platform 2 3scale-amp2/system-rhel8 Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9, rhdh/red-hat-developer-hub-backstage-plugin-lightspeed-backend, rhdh/red-hat-developer-hub-backstage-plugin-orchestrator-backend Red Hat Enterprise Linux 7 firefox Red Hat Enterprise Linux 8 thunderbird Red Hat Enterprise Linux 9 firefox, fdo-init, fdo-client, firefox-x11, thunderbird, fdo-admin-cli, +4 more
    +3 more products
    Red Hat Enterprise Linux 10 firefox, thunderbird Red Hat Trusted Profile Analyzer rhtpa/rhtpa-trustification-service-rhel9 Red Hat Self-service automation portal 2 ansible-automation-platform/automation-portal, ansible-automation-platform/bootc-automation-portal-rhel9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Hardened Images rust, netavark, openshell
    not affected: component 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
no
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 9% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
GitHub 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm multer
<2.3.0
2.3.0

Affected products

  • multer multer

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization

References

Sources

Fencer Vulns 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.