CVE-2026-77037 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in multer. A fix is available for multer — see the affected versions and patch details below.
multer vulnerable to Denial of Service via file descriptor leak on aborted uploads
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-2026-77037.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-77037 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 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. In version 2.2.0, when a disk-backed upload is aborted or truncated before the write stream finishes, multer's disk storage engine removes the visible file but does not close the underlying write file descriptor, leaving a deleted but still open descriptor. A remote attacker able to reach an upload route using the built-in disk storage can send repeated aborted or malformed multipart uploads, each one leaking a file descriptor and retaining disk blocks until the process exits, which can exhaust resources and cause a denial of service. The issue is fixed in multer 2.3.0, which closes the destination write stream on abnormal source termination and defers cleanup until the stream has closed. Upgrade to multer 2.3.0 to remediate.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | multer | ≥ 2.2.0&&< 2.3.0 | 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-2026-77037 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.
A file descriptor leak vulnerability was found in multer, a Node.js middleware for handling multipart/form-data. When using multer's built-in diskStorage engine, aborted or truncated uploads cause the disk storage engine to remove the visible file but fail to close the underlying write file descriptor. A remote…
Upgrade to multer 2.3.0 or later, which properly closes the destination write stream on abnormal source termination and defers cleanup until the stream has closed.Source: Red Hat security advisory for CVE-2026-77037 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Developer Hub 1.10 | rhdh/red-hat-developer-hub-backstage-plugin-orchestrator-backend:1791251282 | RHSA-2026:76788 |
| Red Hat Developer Hub 1.10 | rhdh/rhdh-hub-rhel9:1791311495 | RHSA-2026:79088 |
Frequently Asked Questions
Is CVE-2026-77037 in your dependencies?
Find it across npm, including transitive dependencies.