CVE-2026-77078 is a high-severity (CVSS 7.5) CWE-248 vulnerability in multer. A fix is available for multer — see the affected versions and patch details below.
multer vulnerable to Denial of Service via crafted multipart field names
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-77078.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-77078 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
multernpmDescription
multer is a middleware for handling multipart/form-data in Node.js. A small multipart request containing two specially crafted text field names can cause an uncaught RangeError (Invalid array length) that terminates the Node.js process. The first field uses a very large numeric array index to allocate a maximum-length sparse array, and a second field then pushes past that length, which throws inside the append-field dependency and is not caught by multer. All versions before 2.3.0 are affected, and the issue is a remotely triggerable denial of service. The issue is fixed in multer 2.3.0. Upgrade to multer 2.3.0 to remediate.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | multer | all versions | 2.3.0npm install multer@2.3.0 |
Affected Products
multerexpressjsDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for multer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update multer to 2.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-77078 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This vulnerability affects multiple Red Hat products that bundle or use the multer npm package for handling multipart/form-data in Node.js applications. Products shipping multer versions below 2.3.0 are vulnerable to a remotely triggerable Denial of Service attack. An unauthenticated attacker can crash the Node.js…
Update affected products to versions containing multer 2.3.0 or later. There are no known workarounds - upgrading is the only remediation.Source: Red Hat security advisory for CVE-2026-77078 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Developer Hub 1.10 | rhdh/red-hat-developer-hub-backstage-plugin-lightspeed-backend:1791242697 | RHSA-2026:76788 |
| Red Hat Developer Hub 1.10 | rhdh/rhdh-hub-rhel9:1791311495 | RHSA-2026:79088 |
Frequently Asked Questions
Is CVE-2026-77078 in your dependencies?
Find it across npm, including transitive dependencies.