CVE-2021-33200

Q: What is the severity of CVE-2021-33200?

CVE-2021-33200 has a CVSS score of 7.8 (HIGH). This vulnerability in the Linux kernel's BPF verifier allows incorrect pointer arithmetic limits, enabling out-of-bounds memory access. Attackers can exploit this to read/write kernel memory and escalate privileges to root. Systems running Linux kernel versions up to 5.12.7 are affected.

7.8 HIGH

📋 TL;DR

This vulnerability in the Linux kernel's BPF verifier allows incorrect pointer arithmetic limits, enabling out-of-bounds memory access. Attackers can exploit this to read/write kernel memory and escalate privileges to root. Systems running Linux kernel versions up to 5.12.7 are affected.

💻 Affected Systems

Products:

Linux kernel

Versions: Up to and including 5.12.7

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Requires BPF functionality enabled (default in most distributions).

📦 What is this software?

Linux Kernel by Linux

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⚠️ Risk & Real-World Impact

🔴

Worst Case

Full local privilege escalation to root, allowing complete system compromise and persistence.

🟠

Likely Case

Local privilege escalation enabling attackers to bypass security controls and access sensitive data.

🟢

If Mitigated

Limited impact if proper access controls restrict local user accounts and BPF usage.

🌐 Internet-Facing: LOW - Requires local access to exploit.

🏢 Internal Only: HIGH - Any local user can potentially exploit this to gain root privileges.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires local access and understanding of BPF internals. Proof-of-concept code exists in public repositories.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Linux kernel 5.12.8 and later

Vendor Advisory: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=bb01a1bba579b4b1c5566af24d95f1767859771e

Restart Required: Yes

Instructions:

1. Update kernel to version 5.12.8 or later. 2. Reboot system to load new kernel. 3. Verify kernel version with 'uname -r'.

🔧 Temporary Workarounds

Disable unprivileged BPF

linux

Prevents non-root users from using BPF, which blocks exploitation.

sysctl -w kernel.unprivileged_bpf_disabled=1
echo 'kernel.unprivileged_bpf_disabled = 1' >> /etc/sysctl.conf
sysctl -p

🧯 If You Can't Patch

Restrict local user access to systems
Implement strict privilege separation and monitoring

🔍 How to Verify

Check if Vulnerable:

Run 'uname -r' and check if kernel version is 5.12.7 or earlier.

Check Version:

uname -r

Verify Fix Applied:

Run 'uname -r' and confirm kernel version is 5.12.8 or later.

📡 Detection & Monitoring

Log Indicators:

Kernel panic logs
BPF program loading failures
Unexpected privilege escalation events

Network Indicators:

None - local exploit only

SIEM Query:

source="kernel" AND ("BPF" OR "verifier" OR "privilege escalation")

📊 Metadata

CVE ID: CVE-2021-33200

CVSS v3 Score: 7.8 (HIGH)

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

CWE: CWE-787

Published: May 27, 2021

Last Updated: November 21, 2024

📋 TL;DR

💻 Affected Systems

📦 What is this software?

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H700e Firmware by Netapp

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⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Disable unprivileged BPF

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities