● High · CVSS 8.7

How to Fix CVE-2026-3304: Cwe-459 in multer

Q: What is the CVSS score for CVE-2026-3304?

8.7 (High). Vector: `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`.

Q: Where is the official advisory for CVE-2026-3304?

The vendor advisory is at [https://github.com/expressjs/multer/security/advisories/GHSA-xf7r-hgr6-v32p](https://github.com/expressjs/multer/security/advisories/GHSA-xf7r-hgr6-v32p). The NVD record is at https://nvd.nist.gov/vuln/detail/CVE-2026-3304.

By Sai Kiran Pandrala. Last verified: 2026-05-25.

CVE-2026-3304 is a cwe-459 in expressjs multer. The fix is to apply the vendor patch noted below.

⚡ At a glance


Severity	8.7 (High)
Actively exploited?	No public listing in CISA KEV
Affected	multer 0.0.0 to <2.1.0
Fixed in	See vendor advisory
Type (CWE)	CWE-459

What is CVE-2026-3304?

Multer is a node.js middleware for handling multipart/form-data. A vulnerability in Multer prior to version 2.1.0 allows an attacker to trigger a Denial of Service (DoS) by sending malformed requests, potentially causing resource exhaustion. Users should upgrade to version 2.1.0 to receive a patch. No known workarounds are available. The CVSS base score is 8.7 (High), which puts this in the upper risk band and warrants a fast patch cycle. The official advisory is at https://github.com/expressjs/multer/security/advisories/GHSA-xf7r-hgr6-v32p.

Am I affected?

Check the version of multer you are running and compare it against the Affected row above (multer 0.0.0 to <2.1.0). If your build sits inside the affected range, you must patch.

Run the version check that fits your platform:


# Linux package check
dpkg -s multer 2>/dev/null | grep -i ^Version
rpm -q multer 2>/dev/null
command -v multer >/dev/null && multer --version 2>/dev/null


# Windows (PowerShell)
Get-Package -Name "*multer*" -ErrorAction SilentlyContinue | Select-Object Name, Version
winget list --name "multer" 2>$null

How to fix CVE-2026-3304

Upgrade multer to a patched build: See vendor advisory. The vendor advisory is the source of truth for the exact fixed version.

Ubuntu / Debian


sudo apt-get update
sudo apt-get install --only-upgrade multer
dpkg -s multer | grep -i ^Version

RHEL / CentOS / Rocky / AlmaLinux


sudo dnf upgrade --refresh multer -y
# or for older releases:
sudo yum update multer -y
rpm -q multer

SUSE / openSUSE


sudo zypper refresh
sudo zypper update multer
rpm -q multer

Node.js / npm


# Update the affected package in your project
npm install multer@latest
npm ls multer
npm audit fix

Complete PowerShell remediation script (Windows)


# Fix script for CVE-2026-3304 affecting multer
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-3304-fix-$(Get-Date -Format yyyyMMdd-HHmmss).log"
New-Item -ItemType Directory -Force (Split-Path $LogPath) | Out-Null
Start-Transcript -Path $LogPath -Append

try {
    Write-Host "[1/4] Detect installed version"
    $pkg = Get-Package -Name "*multer*" -ErrorAction SilentlyContinue
    if ($pkg) { $pkg | Format-Table Name, Version }
    else { Write-Host "Not detected via Get-Package; try winget list" }

    Write-Host "[2/4] Backup configuration"
    $backup = "C:\Backup\multer-$(Get-Date -Format yyyyMMdd)"
    New-Item -ItemType Directory -Force $backup | Out-Null
    Get-ChildItem "C:\ProgramData\multer" -ErrorAction SilentlyContinue |
        Copy-Item -Destination $backup -Recurse -Force -ErrorAction SilentlyContinue

    Write-Host "[3/4] Apply the upgrade to See vendor advisory"
    winget upgrade --name "multer" --silent --accept-source-agreements --accept-package-agreements
    if ($LASTEXITCODE -ne 0) {
        # Fallback: pull latest via OS update channel
        Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -ErrorAction SilentlyContinue
        Import-Module PSWindowsUpdate
        Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -IgnoreReboot
    }

    Write-Host "[4/4] Verify the patched build"
    winget list --name "multer"
    Write-Host "Patch applied. Reboot if prompted."
    exit 0
} catch {
    Write-Error "Patch failed: $_"
    exit 1
} finally {
    Stop-Transcript
}

Complete Bash remediation script (Linux)


#!/usr/bin/env bash
# Fix script for CVE-2026-3304 affecting multer
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-3304-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

echo "[1/4] Detect installed version"
if command -v dpkg >/dev/null; then
    dpkg -s multer 2>/dev/null | grep -i ^Version || echo "multer not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q multer || echo "multer not installed via rpm"
fi

echo "[2/4] Backup configuration"
BACKUP="/root/backup-cve-2026-3304-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/multer /etc/multer.d /etc/multer.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Apply the upgrade (target: See vendor advisory)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y multer
elif command -v dnf >/dev/null; then
    dnf upgrade --refresh -y multer
elif command -v yum >/dev/null; then
    yum update -y multer
elif command -v zypper >/dev/null; then
    zypper --non-interactive update multer
fi

echo "[4/4] Verify the patched build"
if command -v dpkg >/dev/null; then
    dpkg -s multer 2>/dev/null | grep -i ^Version
elif command -v rpm >/dev/null; then
    rpm -q multer
fi
echo "Done. Restart any service that loaded the old library."

If you can't patch immediately

Apply at least one of the following inline controls until you can deploy the patched build. None replace the upgrade.

Restrict exposure with nftables (Linux)


# Allow only trusted CIDR to reach the affected service ports
sudo nft add table inet filter 2>/dev/null || true
sudo nft 'add chain inet filter input { type filter hook input priority 0 ; }' 2>/dev/null || true
sudo nft 'add rule inet filter input tcp dport {80, 443} ip saddr != 10.0.0.0/8 drop'
sudo nft list ruleset

Block at the host firewall (Windows)


New-NetFirewallRule -DisplayName "Block-CVE-2026-3304" -Direction Inbound -Action Block -Protocol TCP -LocalPort 80,443 -RemoteAddress Any -Enabled True
Get-NetFirewallRule -DisplayName "Block-CVE-2026-3304"

Disable the affected service (Linux)


sudo systemctl stop multer 2>/dev/null || true
sudo systemctl disable multer 2>/dev/null || true

If the vendor advisory lists an official workaround, prefer that wording verbatim. If no workaround is published, the only safe remediation is the patch.

How to verify the fix worked

After upgrading, confirm the installed version matches the patched build and that no old library is still loaded by a long-running process.


# Linux
dpkg -s multer 2>/dev/null | grep -i ^Version
rpm -q multer 2>/dev/null || true
# Pid map check for old library handles
sudo lsof +c0 2>/dev/null | grep -i "DEL.*lib" || true


# Windows
Get-Package -Name "*multer*" | Select-Object Name, Version
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above See vendor advisory. Restart the affected service (systemctl restart <service> on Linux, or restart the Windows service) so it loads the patched binary.

Frequently asked questions

Other vulnerabilities in the same area that are worth patching alongside this one:

How to Fix CVE-2026-33428: CWE-863: Incorrect Authorization in discourse — CWE-863: Incorrect Authorization in discourse
How to Fix CVE-2026-0865: Critical Vulnerability in CPython — Critical Vulnerability in CPython
How to Fix CVE-2026-2361: Critical Vulnerability in PostgreSQL Anonymizer , Critical Vulnerability in PostgreSQL Anonymizer
How to Fix CVE-2026-21899: Path Traversal in CryptoLib , Path Traversal in CryptoLib
How to Fix CVE-2026-41956: Stack Buffer Overflow in BIG-IP , Stack Buffer Overflow in BIG-IP

Is CVE-2026-3304 actively exploited?

There is no public confirmation of exploitation in the wild listed in CISA KEV at the time of this writing. Patch anyway. Public exploits commonly follow disclosure within weeks.

Do I need to reboot after patching CVE-2026-3304?

For kernel and OS-level updates, yes. For most userland packages a systemctl restart <service> is enough on Linux, and restarting the Windows service or app on Windows. Any process that loaded the old library keeps using it until restarted.

What is the CVSS score for CVE-2026-3304?

8.7 (High). Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N.

Where is the official advisory for CVE-2026-3304?

The vendor advisory is at https://github.com/expressjs/multer/security/advisories/GHSA-xf7r-hgr6-v32p. The NVD record is at https://nvd.nist.gov/vuln/detail/CVE-2026-3304.

References

Official vendor advisory: https://github.com/expressjs/multer/security/advisories/GHSA-xf7r-hgr6-v32p
NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-3304
CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Additional reference: https://www.cve.org/CVERecord?id=CVE-2026-3304
Additional reference: https://github.com/expressjs/multer/commit/739919097dde3921ec31b930e4b9025036fa74ee
Additional reference: https://cna.openjsf.org/security-advisories.html

*Written by Sai Kiran Pandrala. Assembled from the official vendor advisory, NVD record, and CISA KEV listing on 2026-05-25. Always confirm against the vendor's advisory before applying changes in production.*