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Fencer Intel
low 3.7

CVE-2026-77063 json

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

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

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 10%
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

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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-2026-77063 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
2mo ago

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-11).

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 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.