CVE-2022-21716 – CVE-2022-21716 is a memory exhaustion vulnerabi... (How to Fix)

📋 TL;DR

CVE-2022-21716 is a memory exhaustion vulnerability in Twisted's SSH client and server implementations. Attackers can send unlimited data during SSH version negotiation, causing the target system to consume all available memory and crash. This affects any system running vulnerable versions of Twisted with SSH enabled.

💻 Affected Systems

Products:

Twisted

Versions: All versions prior to 22.2.0

Operating Systems: All operating systems running Python with Twisted

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects Twisted installations with SSH functionality enabled (twisted.conch).

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete denial of service through memory exhaustion, potentially causing system crashes and service unavailability.

🟠

Likely Case

Service disruption and denial of service affecting SSH connectivity and dependent applications.

🟢

If Mitigated

Limited impact with proper network segmentation and monitoring, but still vulnerable to DoS from authorized network segments.

🌐 Internet-Facing: HIGH - SSH services exposed to the internet are directly vulnerable to simple DoS attacks.

🏢 Internal Only: MEDIUM - Internal SSH services are vulnerable to authenticated or network-accessible attackers.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: CONFIRMED

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Simple network command (nc -rv localhost 22 < /dev/zero) can trigger the vulnerability. No authentication required.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 22.2.0

Vendor Advisory: https://github.com/twisted/twisted/security/advisories/GHSA-rv6r-3f5q-9rgx

Restart Required: Yes

Instructions:

1. Upgrade Twisted to version 22.2.0 or later using pip: pip install --upgrade twisted>=22.2.0
2. Restart all services using Twisted SSH functionality
3. Verify the upgrade with: python -c "import twisted; print(twisted.__version__)"

🔧 Temporary Workarounds

No known workarounds

all

The vendor advisory states there are no known workarounds. Patching is required.

🧯 If You Can't Patch

Implement network-level controls to restrict SSH access to trusted sources only
Monitor memory usage on systems running Twisted SSH services and implement alerting for abnormal consumption

🔍 How to Verify

Check if Vulnerable:

Check Twisted version: python -c "import twisted; print(twisted.__version__)" - if version is less than 22.2.0 and SSH functionality is enabled, system is vulnerable.

Check Version:

python -c "import twisted; print(twisted.__version__)"

Verify Fix Applied:

Verify Twisted version is 22.2.0 or higher: python -c "import twisted; print(twisted.__version__)" should show 22.2.0 or greater.

📡 Detection & Monitoring

Log Indicators:

Unusually large SSH version strings in logs
Memory exhaustion alerts
SSH service crashes or restarts

Network Indicators:

Excessive data sent during SSH version negotiation
Unusual traffic patterns to SSH port 22

SIEM Query:

source="*ssh*" AND (message="*memory*" OR message="*exhaust*" OR message="*crash*")

📊 Metadata

CVE ID: CVE-2022-21716

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-120

Published: March 3, 2022

Last Updated: November 25, 2024

🔗 References

https://github.com/twisted/twisted/commit/89c395ee794e85a9657b112c4351417850330ef9 Patch,Third Party Advisory
https://github.com/twisted/twisted/releases/tag/twisted-22.2.0 Release Notes,Third Party Advisory
https://github.com/twisted/twisted/security/advisories/GHSA-rv6r-3f5q-9rgx Exploit,Patch,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/03/msg00009.html Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7U6KYDTOLPICAVSR34G2WRYLFBD2YW5K/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GLKHA6WREIVAMBQD7KKWYHPHGGNKMAG6/
https://security.gentoo.org/glsa/202301-02 Third Party Advisory
https://twistedmatrix.com/trac/ticket/10284 Issue Tracking,Vendor Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html Patch,Third Party Advisory
https://github.com/twisted/twisted/commit/89c395ee794e85a9657b112c4351417850330ef9 Patch,Third Party Advisory
https://github.com/twisted/twisted/releases/tag/twisted-22.2.0 Release Notes,Third Party Advisory
https://github.com/twisted/twisted/security/advisories/GHSA-rv6r-3f5q-9rgx Exploit,Patch,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/03/msg00009.html Mailing List,Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7U6KYDTOLPICAVSR34G2WRYLFBD2YW5K/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GLKHA6WREIVAMBQD7KKWYHPHGGNKMAG6/
https://security.gentoo.org/glsa/202301-02 Third Party Advisory
https://twistedmatrix.com/trac/ticket/10284 Issue Tracking,Vendor Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html Patch,Third Party Advisory

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