CVE-2020-9283 – This vulnerability in Go's SSH package allows a... (How to Fix)

Q: What is the severity of CVE-2020-9283?

CVE-2020-9283 has a CVSS score of 7.5 (HIGH). This vulnerability in Go's SSH package allows attackers to cause denial of service through panic during signature verification. Both SSH servers accepting public keys and SSH clients can be attacked. Systems using affected versions of golang.org/x/crypto are vulnerable.

📋 TL;DR

This vulnerability in Go's SSH package allows attackers to cause denial of service through panic during signature verification. Both SSH servers accepting public keys and SSH clients can be attacked. Systems using affected versions of golang.org/x/crypto are vulnerable.

💻 Affected Systems

Products:

Go applications using golang.org/x/crypto/ssh package
SSH servers built with Go
SSH clients built with Go

Versions: All versions before v0.0.0-20200220183623-bac4c82f6975

Operating Systems: All operating systems running Go applications

Default Config Vulnerable: ⚠️ Yes

Notes: Any Go application using the SSH package for authentication with public keys is vulnerable. Both client and server implementations are affected.

📦 What is this software?

Debian Linux by Debian

View all CVEs affecting Debian Linux →

Package Ssh by Golang

View all CVEs affecting Package Ssh →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete SSH service disruption causing denial of service to all SSH connections, potentially affecting remote administration and automated processes.

🟠

Likely Case

Targeted DoS attacks against SSH services causing service interruptions and requiring restarts.

🟢

If Mitigated

Minimal impact with proper monitoring and rapid recovery procedures in place.

🌐 Internet-Facing: HIGH - SSH servers exposed to the internet are directly attackable by any client.

🏢 Internal Only: MEDIUM - Internal SSH services could be attacked by compromised internal systems or malicious insiders.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Public exploit code exists in Packet Storm. Attack requires ability to initiate SSH connection but no authentication credentials.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: v0.0.0-20200220183623-bac4c82f6975 or later

Vendor Advisory: https://groups.google.com/forum/#!topic/golang-announce/3L45YRc91SY

Restart Required: Yes

Instructions:

1. Update golang.org/x/crypto dependency to v0.0.0-20200220183623-bac4c82f6975 or later. 2. Rebuild and redeploy affected Go applications. 3. Restart SSH services using the updated binaries.

🔧 Temporary Workarounds

Disable public key authentication

linux

Temporarily disable public key authentication in SSH configuration to prevent exploitation

For OpenSSH servers: Edit /etc/ssh/sshd_config and set 'PubkeyAuthentication no'
Restart SSH service: systemctl restart sshd

🧯 If You Can't Patch

Implement network segmentation to restrict SSH access to trusted sources only
Deploy rate limiting on SSH connections to mitigate DoS impact

🔍 How to Verify

Check if Vulnerable:

Check Go module dependencies for golang.org/x/crypto version. If using go.mod: grep 'golang.org/x/crypto' go.mod

Check Version:

go list -m golang.org/x/crypto

Verify Fix Applied:

Verify the updated version appears in go.mod or vendor directory: grep -r 'bac4c82f6975' vendor/golang.org/x/crypto/

📡 Detection & Monitoring

Log Indicators:

SSH service crashes or restarts
Panic stack traces in application logs containing 'ssh' package references
Multiple failed SSH connections from single source

Network Indicators:

Unusual SSH connection patterns causing service disruption
SSH connections with malformed public key data

SIEM Query:

source="sshd" AND ("panic" OR "crash" OR "restarting")

📊 Metadata

CVE ID: CVE-2020-9283

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-347

Published: February 20, 2020

Last Updated: November 21, 2024

🔗 References

http://packetstormsecurity.com/files/156480/Go-SSH-0.0.2-Denial-Of-Service.html Exploit,Third Party Advisory,VDB Entry
https://groups.google.com/forum/#%21topic/golang-announce/3L45YRc91SY
https://lists.debian.org/debian-lts-announce/2020/10/msg00014.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2020/11/msg00027.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2020/11/msg00031.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/06/msg00017.html
http://packetstormsecurity.com/files/156480/Go-SSH-0.0.2-Denial-Of-Service.html Exploit,Third Party Advisory,VDB Entry
https://groups.google.com/forum/#%21topic/golang-announce/3L45YRc91SY
https://lists.debian.org/debian-lts-announce/2020/10/msg00014.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2020/11/msg00027.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2020/11/msg00031.html Mailing List,Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/06/msg00017.html

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