⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● High · CVSS 7.8 ⚠ ACTIVELY EXPLOITED — CISA KEV

How to Fix CVE-2020-3837: Out-of-bounds Write in Ios

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

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 7.8 - High
Actively exploited?Yes, listed in CISA KEV (added 2022-06-27)
AffectediOS: unspecified < iOS 13.3.1 and iPadOS 13.3.1; macOS: unspecified < macOS Catalina 10.15.3; tvOS: unspecified < tvOS 13.3.1; watchOS: unspecified < watchOS 6.1.2
Fixed inSee vendor advisory for the patched build
Type (CWE)CWE-787 Out-of-bounds Write
Patch immediately. CISA's Known Exploited Vulnerabilities catalog lists this CVE, which means active exploitation has been confirmed. CISA KEV entry added 2022-06-27, federal due date 2022-07-18.

What is CVE-2020-3837?

CVE-2020-3837 is a out-of-bounds write in Ios from Apple. A memory corruption issue was addressed with improved memory handling. This issue is fixed in iOS 13.3.1 and iPadOS 13.3.1, macOS Catalina 10.15.3, tvOS 13.3.1, watchOS 6.1.2. An application may be able to execute arbitrary code with kernel privileges.

Why this CVE matters

This CVE sits on CISA's Known Exploited Vulnerabilities catalog, which only happens after active exploitation is observed in the wild. The out-of-bounds write class of flaw gives attackers a reliable foothold against vulnerable instances of Ios. If your deployment matches the affected versions, treat any window of unpatched exposure as compromise-likely and review logs accordingly.

Am I affected?

Run the version check that matches your platform. If the installed build sits inside the affected range from the table above, the fix applies to you.


# Linux package check
dpkg -s ios 2>/dev/null | grep -i version    # Debian / Ubuntu
rpm -q ios 2>/dev/null                       # RHEL / Rocky

How to fix CVE-2020-3837

Apply the patched build the vendor names in the advisory. The commands below are starting points keyed to common platforms - adapt the package name and target version to your environment.

Ubuntu / Debian


sudo apt-get update
sudo apt-get install --only-upgrade ios
# verify the package version matches the fixed release in the advisory
dpkg -s ios | grep -i version

RHEL / CentOS / Rocky / AlmaLinux


sudo dnf upgrade --refresh ios -y
rpm -q ios

Container image


# Vendor advisory: https://support.apple.com/HT210919
# Pull the patched base image and rebuild
docker pull <your-registry>/ios:<patched-tag>
docker build -t <your-app>:patched .
docker stop <your-app> && docker rm <your-app>
docker run -d --name <your-app> <your-app>:patched

PowerShell detect/upgrade/verify/log (Windows)


# CVE-2020-3837 remediation runner — adapt the version checks to your environment.
$log = "C:\Logs\CVE-2020-3837-fix.log"
New-Item -ItemType Directory -Force -Path (Split-Path $log) | Out-Null
function Write-Log($msg) { "$(Get-Date -Format s) $msg" | Out-File $log -Append }

try {
    Write-Log "Detect: checking installed product"
    $installed = Get-CimInstance Win32_Product -ErrorAction SilentlyContinue |
        Where-Object { $_.Name -match 'iOS' }
    if (-not $installed) { Write-Log "Product not installed; nothing to do"; return }
    Write-Log "Found version $($installed.Version)"

    Write-Log "Backup: copying program files and registry hive"
    $stamp = Get-Date -Format yyyyMMdd-HHmm
    $backup = "C:\Backup\CVE-2020-3837-$stamp"
    New-Item -ItemType Directory -Force -Path $backup | Out-Null
    Copy-Item $installed.InstallLocation $backup -Recurse -ErrorAction SilentlyContinue
    reg export HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall "$backup\uninstall.reg" /y | Out-Null

    Write-Log "Upgrade: install patched build via vendor MSI / Windows Update"
    # Example MSI:  Start-Process msiexec.exe -ArgumentList '/i C:\Patches\iOS-patched.msi /qn /norestart' -Wait
    Install-WindowsUpdate -AcceptAll -AutoReboot -ErrorAction SilentlyContinue

    Write-Log "Verify: re-reading product version"
    $after = Get-CimInstance Win32_Product | Where-Object { $_.Name -match 'iOS' }
    Write-Log "Post-patch version: $($after.Version)"
    if ($after.Version -ne $installed.Version) { Write-Log "SUCCESS: version changed" } else { Write-Log "WARN: version unchanged - check vendor advisory" }
} catch {
    Write-Log "ERROR: $_"
    throw
}

Bash detect/upgrade/verify/log (Linux)


#!/usr/bin/env bash
# CVE-2020-3837 remediation runner. Re-runnable, exits non-zero on failure.
set -euo pipefail
log() { printf '%s %s\n' "$(date -Is)" "$*" | tee -a /var/log/cve-2020-3837-fix.log; }

log "Detect: current ios version"
if command -v dpkg >/dev/null 2>&1; then
    current=$(dpkg-query -W -f='${Version}' ios 2>/dev/null || echo "not-installed")
elif command -v rpm >/dev/null 2>&1; then
    current=$(rpm -q --qf '%{VERSION}-%{RELEASE}' ios 2>/dev/null || echo "not-installed")
else
    current="unknown"
fi
log "Current: $current"

log "Backup: snapshotting config"
backup="/var/backups/cve-2020-3837-$(date +%Y%m%d-%H%M)"
mkdir -p "$backup"
[ -d /etc/ios ] && cp -a /etc/ios "$backup/" || true

log "Upgrade: applying vendor patch"
if command -v apt-get >/dev/null 2>&1; then
    sudo apt-get update -qq
    sudo apt-get install -y --only-upgrade ios
elif command -v dnf >/dev/null 2>&1; then
    sudo dnf upgrade -y ios
elif command -v yum >/dev/null 2>&1; then
    sudo yum update -y ios
fi

log "Verify: re-reading ios version"
if command -v dpkg >/dev/null 2>&1; then
    after=$(dpkg-query -W -f='${Version}' ios)
else
    after=$(rpm -q --qf '%{VERSION}-%{RELEASE}' ios)
fi
log "After: $after"

if [ "$after" != "$current" ]; then
    log "SUCCESS: ios upgraded"
else
    log "WARN: version unchanged. Confirm the patched build is in your repository."
    exit 1
fi

After the upgrade, restart any service that loads the patched binary so the new code is actually running.

If you can't patch immediately

Patching is the only durable fix. These mitigations cut exposure while the change window is scheduled, they do not remove the vulnerability.


# No vendor-published workaround for CVE-2020-3837 beyond the patch.
# Reduce the blast radius until the patched build is deployed:
#   - Restrict network access to the affected service to known admin hosts
#   - Disable the vulnerable feature in config if the product allows it
#   - Increase logging on the affected endpoints and watch for IoCs

How to verify the fix worked

After applying the patched build, confirm the version string matches the fixed release named in the Apple advisory.


dpkg -s ios | grep -i version       # Debian / Ubuntu
rpm -q ios                          # RHEL / Rocky

Run an authenticated vulnerability scan with a current signature set and confirm the scanner no longer flags CVE-2020-3837. For internet-facing deployments that were unpatched during the disclosure window, review logs for the affected endpoints over the full exposure period and rotate any credentials the vulnerable process could touch.

Frequently asked questions

Is CVE-2020-3837 being exploited in the wild?

Yes. CISA added CVE-2020-3837 to the Known Exploited Vulnerabilities catalog, which means active exploitation has been confirmed.

Will a firewall rule or WAF signature fully mitigate CVE-2020-3837?

No. Network-layer filters slow opportunistic scanners and block a subset of payloads, but a focused attacker who knows the bug will work around them. The vendor patch is the only durable fix.

Do I need to assume compromise if the affected service was internet-facing and unpatched?

For a CVE that CISA confirms is under active exploitation, yes. Review logs for the affected endpoints over the entire exposure window, rotate credentials the vulnerable process could read, and look for unexpected accounts, scheduled tasks, or outbound connections.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*