CVE-2021-22600: Netapp 8300 Privilege Escalation Flaw

CVE-2021-22600 Overview

CVE-2021-22600 is a double free vulnerability in the Linux kernel's packet_set_ring() function located in net/packet/af_packet.c. This memory corruption flaw can be exploited by local users through crafted syscalls to achieve privilege escalation or cause denial of service conditions. The vulnerability has been added to CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild.

Critical Impact

Local attackers with limited privileges can exploit this double free vulnerability to escalate privileges to root or crash the system, making it a significant threat to multi-tenant environments and shared hosting platforms.

Affected Products

• Linux Kernel (multiple versions)
• Debian Linux 9.0 and 10.0
• NetApp 8300/8700 Firmware
• NetApp A400/C400 Firmware
• NetApp H410C/H410S Firmware
• NetApp H300S/H500S/H700S Firmware

Discovery Timeline

• 2022-01-26 - CVE-2021-22600 published to NVD
• 2025-10-24 - Last updated in NVD database

Technical Details for CVE-2021-22600

Vulnerability Analysis

The vulnerability exists in the AF_PACKET socket implementation within the Linux kernel. The packet_set_ring() function in net/packet/af_packet.c contains a double free bug that occurs during the handling of packet ring buffers. This flaw is classified as CWE-415 (Double Free), which happens when memory is freed more than once, leading to memory corruption.

When a local user sends specially crafted syscalls to the affected function, the kernel may attempt to free the same memory region twice. This memory corruption can be leveraged to overwrite critical kernel data structures, enabling an attacker to gain elevated privileges or trigger a kernel panic resulting in denial of service.

The attack requires local access to the system and low privileges, but no user interaction is needed. While the attack complexity is high, successful exploitation can result in complete compromise of confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2021-22600 lies in improper memory management within the packet_set_ring() function. The function fails to properly track the allocation state of packet ring buffers, leading to a scenario where the same memory block can be freed multiple times. This double free condition corrupts the kernel's memory allocator metadata, which can be exploited by an attacker to gain control over subsequent memory allocations and achieve arbitrary code execution in kernel context.

Attack Vector

The attack vector for CVE-2021-22600 is local, requiring the attacker to have authenticated access to the target system. The exploitation process involves:

1. Creating an AF_PACKET socket with appropriate permissions
2. Sending crafted syscalls to manipulate the packet ring buffer state
3. Triggering the double free condition through carefully timed operations
4. Leveraging the corrupted memory state to overwrite kernel structures
5. Achieving privilege escalation to root or causing system crash

The double free vulnerability can be triggered through the setsockopt() syscall with the PACKET_RX_RING or PACKET_TX_RING options. The attacker must carefully manipulate the ring buffer configuration to create the conditions necessary for the memory to be freed twice.

Detection Methods for CVE-2021-22600

Indicators of Compromise

• Unusual AF_PACKET socket activity from non-privileged users
• Kernel crash dumps indicating double free corruption in slab allocator
• Unexpected privilege escalation events for local user accounts
• Anomalous syscall patterns targeting packet socket operations

Detection Strategies

• Monitor for suspicious setsockopt() calls with PACKET_RX_RING or PACKET_TX_RING options
• Deploy kernel exploit detection mechanisms that identify memory corruption attempts
• Utilize Linux Audit Framework to track AF_PACKET socket creation and manipulation
• Implement EDR solutions like SentinelOne that can detect privilege escalation attempts

Monitoring Recommendations

• Enable kernel auditing for CAP_NET_RAW capability usage
• Monitor system logs for KASAN (Kernel Address Sanitizer) reports if enabled
• Track user privilege changes and correlate with socket-related activity
• Review crash dumps for patterns consistent with double free exploitation

How to Mitigate CVE-2021-22600

Immediate Actions Required

• Upgrade the Linux kernel to a version that includes commit ec6af094ea28f0f2dda1a6a33b14cd57e36a9755 or later
• Apply security patches from your Linux distribution vendor immediately
• Restrict CAP_NET_RAW capability to trusted users only
• Monitor for exploitation attempts using endpoint detection solutions

Patch Information

The vulnerability has been addressed in the upstream Linux kernel. The fix is available in commit ec6af094ea28f0f2dda1a6a33b14cd57e36a9755. Distribution-specific patches are available:

• Debian has released DSA-5096 addressing this vulnerability
• Debian LTS users should refer to the LTS announcement
• NetApp users should consult the NetApp Security Advisory

Workarounds

• Disable unprivileged user namespaces if not required: sysctl -w kernel.unprivileged_userns_clone=0
• Restrict AF_PACKET socket creation using seccomp filters
• Limit CAP_NET_RAW capability using capability bounding sets
• Implement network namespace isolation to contain potential exploitation

# Restrict CAP_NET_RAW capability for non-root users
# Add to /etc/sysctl.conf or /etc/sysctl.d/99-security.conf
kernel.unprivileged_userns_clone = 0

# Apply immediately
sysctl -p

# Verify the setting
sysctl kernel.unprivileged_userns_clone