CVE-2021-20319 – CVE-2021-20319 is an improper signature verific... (How to Fix)

Q: What is the severity of CVE-2021-20319?

CVE-2021-20319 has a CVSS score of 7.8 (HIGH). CVE-2021-20319 is an improper signature verification vulnerability in coreos-installer that allows specially crafted gzip installation images to bypass signature checks. This enables attackers who can modify installation images to install unsigned content and gain full access to nodes being installed. Affected users include anyone using coreos-installer to deploy CoreOS/RHEL CoreOS systems.

📋 TL;DR

CVE-2021-20319 is an improper signature verification vulnerability in coreos-installer that allows specially crafted gzip installation images to bypass signature checks. This enables attackers who can modify installation images to install unsigned content and gain full access to nodes being installed. Affected users include anyone using coreos-installer to deploy CoreOS/RHEL CoreOS systems.

💻 Affected Systems

Products:

coreos-installer

Versions: Versions before 0.10.0

Operating Systems: Fedora CoreOS, Red Hat Enterprise Linux CoreOS

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects installations using gzip-compressed images. Systems already deployed are not vulnerable.

📦 What is this software?

Coreos Installer by Redhat

View all CVEs affecting Coreos Installer →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Full compromise of newly deployed nodes with root access, enabling persistent backdoors, data theft, and lateral movement within the infrastructure.

🟠

Likely Case

Supply chain attack where attackers compromise installation media or distribution channels to deploy malicious images to multiple systems.

🟢

If Mitigated

No impact if using verified installation sources and updated installer versions with proper signature validation.

🌐 Internet-Facing: MEDIUM - Requires attacker to compromise installation media distribution or intercept downloads, but successful exploitation yields high impact.

🏢 Internal Only: MEDIUM - Internal attackers with access to modify installation images could compromise new deployments.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires ability to modify installation images before they're used. Exploitation depends on compromising image distribution channels or local access to modify images.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: coreos-installer 0.10.0 and later

Vendor Advisory: https://github.com/coreos/coreos-installer/security/advisories/GHSA-3r3g-g73x-g593

Restart Required: No

Instructions:

1. Update coreos-installer to version 0.10.0 or later using your package manager. 2. For RHEL CoreOS: 'sudo dnf update coreos-installer'. 3. For Fedora CoreOS: Update via standard update mechanisms or reinstall with updated installer.

🔧 Temporary Workarounds

Use uncompressed or differently compressed images

linux

Avoid using gzip-compressed installation images until patched

coreos-installer install --image-file uncompressed.raw /dev/sdX

Verify image signatures manually

linux

Manually verify image signatures before installation

gpg --verify image.sig image.gz
sha256sum -c image.sha256

🧯 If You Can't Patch

Only use installation images from trusted, verified sources with intact signatures
Implement strict access controls on installation media storage and distribution channels

🔍 How to Verify

Check if Vulnerable:

Check coreos-installer version: 'coreos-installer --version' or 'rpm -q coreos-installer'. If version is below 0.10.0, system is vulnerable.

Check Version:

coreos-installer --version

Verify Fix Applied:

Confirm version is 0.10.0 or higher: 'coreos-installer --version | grep -q "0\.1[0-9]\+" && echo "Patched"'

📡 Detection & Monitoring

Log Indicators:

Failed signature verification attempts
Unexpected installation source changes
Installation from unverified locations

Network Indicators:

Downloads of installation images from unusual sources
Unencrypted transfer of installation media

SIEM Query:

source="coreos-installer" AND ("signature" OR "verification") AND ("failed" OR "bypass" OR "invalid")

📊 Metadata

CVE ID: CVE-2021-20319

CVSS v3 Score: 7.8 (HIGH)

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

CWE: CWE-347

Published: March 4, 2022

Last Updated: November 21, 2024

🔗 References

https://bugzilla.redhat.com/show_bug.cgi?id=2011862 Issue Tracking,Vendor Advisory
https://github.com/coreos/coreos-installer/pull/659/commits/ad243c6f0eff2835b2da56ca5f7f33af76253c89 Patch,Third Party Advisory
https://github.com/coreos/coreos-installer/security/advisories/GHSA-3r3g-g73x-g593 Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2011862 Issue Tracking,Vendor Advisory
https://github.com/coreos/coreos-installer/pull/659/commits/ad243c6f0eff2835b2da56ca5f7f33af76253c89 Patch,Third Party Advisory
https://github.com/coreos/coreos-installer/security/advisories/GHSA-3r3g-g73x-g593 Third Party Advisory

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🔗 Related Vulnerabilities

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