CVE-2021-29873 – CVE-2021-29873 is a restricted shell escape vul... (How to Fix)

Q: What is the severity of CVE-2021-29873?

CVE-2021-29873 has a CVSS score of 8.1 (HIGH). CVE-2021-29873 is a restricted shell escape vulnerability in IBM Flash System 900 that allows authenticated attackers to break out of restricted shells, potentially accessing sensitive information and causing denial of service. This affects administrators and users with authenticated access to the Flash System 900 management interface.

📋 TL;DR

CVE-2021-29873 is a restricted shell escape vulnerability in IBM Flash System 900 that allows authenticated attackers to break out of restricted shells, potentially accessing sensitive information and causing denial of service. This affects administrators and users with authenticated access to the Flash System 900 management interface.

💻 Affected Systems

Products:

IBM Flash System 900

Versions: All versions prior to 1.6.1.0

Operating Systems: IBM Flash System OS

Default Config Vulnerable: ⚠️ Yes

Notes: Requires authenticated access to the Flash System management interface.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Authenticated attacker gains full system access, exfiltrates sensitive data, and causes complete system outage.

🟠

Likely Case

Authenticated user escapes restricted shell to access unauthorized files and disrupt management functions.

🟢

If Mitigated

Attack fails due to proper access controls and network segmentation limiting shell access.

🌐 Internet-Facing: MEDIUM - Only if management interface is exposed to internet with authenticated access.

🏢 Internal Only: HIGH - Internal authenticated users can exploit this vulnerability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: LOW

Requires authenticated access but shell escape techniques are typically straightforward once authenticated.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 1.6.1.0 and later

Vendor Advisory: https://www.ibm.com/support/pages/node/6497111

Restart Required: Yes

Instructions:

1. Backup configuration and data. 2. Download firmware 1.6.1.0 or later from IBM Fix Central. 3. Apply firmware update via management interface. 4. Reboot system as required. 5. Verify update completed successfully.

🔧 Temporary Workarounds

Restrict Management Access

all

Limit access to Flash System management interface to only trusted administrators using network segmentation and firewall rules.

Implement Least Privilege

all

Review and minimize user accounts with shell access, implement strict RBAC for Flash System management.

🧯 If You Can't Patch

Implement strict network segmentation to isolate Flash System management interface
Enable detailed logging and monitoring for shell access attempts and unusual activities

🔍 How to Verify

Check if Vulnerable:

Check current firmware version via Flash System management GUI or CLI. If version is below 1.6.1.0, system is vulnerable.

Check Version:

ssh admin@flashsystem 'version' or check via web management interface

Verify Fix Applied:

Confirm firmware version is 1.6.1.0 or later via management interface and verify no shell escape is possible from restricted shells.

📡 Detection & Monitoring

Log Indicators:

Unusual shell commands from authenticated users
Multiple failed shell escape attempts
Access to restricted files or directories

Network Indicators:

Unusual SSH traffic patterns to Flash System management IP
Multiple authentication attempts followed by shell commands

SIEM Query:

source="flashsystem_logs" AND (event="shell_escape" OR command="chroot" OR command="bash" OR command="sh")

📊 Metadata

CVE ID: CVE-2021-29873

CVSS v3 Score: 8.1 (HIGH)

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

Published: October 21, 2021

Last Updated: November 21, 2024

🔗 References

https://exchange.xforce.ibmcloud.com/vulnerabilities/206229 VDB Entry,Vendor Advisory
https://www.ibm.com/support/pages/node/6497111 Patch,Vendor Advisory
https://www.ibm.com/support/pages/node/6507091 Patch,Vendor Advisory
https://exchange.xforce.ibmcloud.com/vulnerabilities/206229 VDB Entry,Vendor Advisory
https://www.ibm.com/support/pages/node/6497111 Patch,Vendor Advisory
https://www.ibm.com/support/pages/node/6507091 Patch,Vendor Advisory

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