CVE-2020-11612 – CVE-2020-11612 is a memory allocation vulnerabi... (How to Fix)

Q: What is the severity of CVE-2020-11612?

CVE-2020-11612 has a CVSS score of 7.5 (HIGH). CVE-2020-11612 is a memory allocation vulnerability in Netty's ZlibDecoders that allows attackers to cause denial of service through memory exhaustion. Attackers can send specially crafted Zlib-encoded byte streams to force Netty servers to allocate all available memory to a single decoder. This affects any application using Netty 4.1.x before 4.1.46 with Zlib decoding enabled.

📋 TL;DR

CVE-2020-11612 is a memory allocation vulnerability in Netty's ZlibDecoders that allows attackers to cause denial of service through memory exhaustion. Attackers can send specially crafted Zlib-encoded byte streams to force Netty servers to allocate all available memory to a single decoder. This affects any application using Netty 4.1.x before 4.1.46 with Zlib decoding enabled.

💻 Affected Systems

Products:

Netty

Versions: Netty 4.1.x before 4.1.46

Operating Systems: All operating systems running Java applications using vulnerable Netty versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects systems using ZlibDecoders. Applications must be configured to use Zlib decoding for this vulnerability to be exploitable.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete denial of service as the server exhausts all available memory, causing crashes and service unavailability.

🟠

Likely Case

Service degradation or temporary unavailability due to memory exhaustion, requiring server restarts.

🟢

If Mitigated

Minimal impact if memory limits are enforced or the vulnerability is patched.

🌐 Internet-Facing: HIGH - Attackers can exploit this remotely without authentication by sending malicious payloads.

🏢 Internal Only: MEDIUM - Internal attackers could still exploit this, but requires network access to vulnerable services.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

The exploit is straightforward - sending a specially crafted Zlib-encoded byte stream. Public references and patches demonstrate the attack vector.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Netty 4.1.46 and later

Vendor Advisory: https://github.com/netty/netty/security/advisories/GHSA-5mcr-gq6c-3hq2

Restart Required: Yes

Instructions:

1. Update Netty dependency to version 4.1.46 or later. 2. Update your project's pom.xml or build.gradle to reference the fixed version. 3. Rebuild and redeploy your application. 4. Restart affected services.

🔧 Temporary Workarounds

Disable Zlib decoding

all

If Zlib decoding is not required, disable it in your Netty configuration to remove the attack vector.

Configure your Netty server/channel to not use ZlibDecoders

Implement memory limits

all

Configure JVM memory limits and monitoring to detect and prevent memory exhaustion attacks.

-Xmx to set maximum heap size
Use monitoring tools to track memory usage

🧯 If You Can't Patch

Implement network-level controls to filter or limit incoming Zlib-encoded traffic
Deploy memory monitoring and alerting to detect memory exhaustion patterns

🔍 How to Verify

Check if Vulnerable:

Check your project's dependencies for Netty version 4.1.0 through 4.1.45. Use: mvn dependency:tree | grep netty or gradle dependencies | grep netty

Check Version:

java -cp "your-application.jar" io.netty.util.Version

Verify Fix Applied:

Verify Netty version is 4.1.46 or higher. Test with sample Zlib-encoded payloads while monitoring memory usage.

📡 Detection & Monitoring

Log Indicators:

OutOfMemoryError in logs
High memory usage patterns
Unusually large incoming payloads

Network Indicators:

Large Zlib-encoded payloads to Netty endpoints
Spike in network traffic to specific ports

SIEM Query:

source="application.logs" AND ("OutOfMemoryError" OR "java.lang.OutOfMemoryError") AND process="java"

📊 Metadata

CVE ID: CVE-2020-11612

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-770

Published: April 7, 2020

Last Updated: November 21, 2024

🔗 References

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