CVE-2020-7457: FreeBSD Race Condition Vulnerability

CVE-2020-7457 Overview

CVE-2020-7457 is a use-after-free vulnerability caused by a race condition in the FreeBSD kernel's IPv6 socket option handler. Specifically, the IPV6_2292PKTOPTIONS socket option set handler lacks proper synchronization, allowing a malicious application to exploit the race condition to modify memory after it has been freed. This can potentially lead to arbitrary code execution with elevated privileges.

Critical Impact

Successful exploitation of this vulnerability could allow a local attacker to escalate privileges and execute arbitrary code at kernel level, potentially leading to complete system compromise.

Affected Products

• FreeBSD 12.1-STABLE before r359565
• FreeBSD 12.1-RELEASE before p7 (including p1 through p6)
• FreeBSD 11.4-STABLE before r362975
• FreeBSD 11.4-RELEASE before p1
• FreeBSD 11.3-RELEASE before p11 (including all prior patch levels)

Discovery Timeline

• 2020-07-09 - CVE-2020-7457 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-7457

Vulnerability Analysis

This vulnerability exists within the FreeBSD kernel's handling of the IPV6_2292PKTOPTIONS socket option, which is part of the IPv6 implementation. The core issue stems from a missing synchronization mechanism that creates a time-of-check time-of-use (TOCTOU) race condition. When the socket option handler processes requests, it fails to properly lock or synchronize access to memory structures, creating a window where freed memory can be accessed and modified.

The attack requires network access but involves high complexity due to the need to precisely time the race condition. However, because no user interaction is required and the vulnerability affects confidentiality, integrity, and availability at a high level, successful exploitation can be devastating. An attacker who wins the race can corrupt kernel memory structures, potentially gaining the ability to execute arbitrary code with kernel privileges.

Root Cause

The root cause is a missing synchronization primitive (such as a mutex lock or spinlock) in the ip6_setpktopt() function within the IPv6 packet options handling code. When multiple threads or processes access the socket option handler concurrently, the lack of proper locking allows one execution path to free memory while another still holds a reference to it. This classic race condition pattern violates memory safety guarantees and creates the use-after-free condition.

Attack Vector

The attack vector is network-accessible, meaning a malicious application on the system can trigger the vulnerability through socket operations. The attacker must create a scenario where the race condition can be reliably triggered:

1. The attacker opens an IPv6 socket and configures it to use the legacy IPV6_2292PKTOPTIONS option
2. Multiple threads are spawned to simultaneously manipulate socket options
3. By carefully timing these operations, the attacker can cause the socket option handler to free memory while another thread still references it
4. The attacker then sprays the heap with controlled data to reclaim the freed memory
5. Subsequent use of the stale pointer allows arbitrary memory modification, leading to privilege escalation

A public exploit demonstrating this technique is available on Packet Storm that achieves local privilege escalation through this vulnerability.

Detection Methods for CVE-2020-7457

Indicators of Compromise

• Unusual crash patterns in the FreeBSD kernel related to IPv6 processing or socket operations
• Kernel panic messages referencing memory corruption in networking subsystem
• Unexpected privilege escalation attempts from unprivileged user processes
• Multiple concurrent IPv6 socket operations from suspicious processes

Detection Strategies

• Monitor kernel logs for panics or memory corruption errors in IPv6-related code paths
• Implement system call auditing to detect unusual patterns of setsockopt() calls with IPV6_2292PKTOPTIONS
• Deploy kernel-level integrity monitoring to detect unauthorized modifications
• Utilize SentinelOne's behavioral AI to identify anomalous process behavior consistent with race condition exploitation

Monitoring Recommendations

• Enable FreeBSD audit subsystem to log all socket option operations
• Configure alerting for kernel crashes or unexpected reboots that may indicate exploitation attempts
• Monitor for processes making rapid, repetitive IPv6 socket operations
• Implement network segmentation to limit exposure of vulnerable systems

How to Mitigate CVE-2020-7457

Immediate Actions Required

• Upgrade to FreeBSD 12.1-RELEASE-p7 or later for the 12.x branch
• Upgrade to FreeBSD 11.4-RELEASE-p1 or later for the 11.4 branch
• Upgrade to FreeBSD 11.3-RELEASE-p11 or later for the 11.3 branch
• If immediate patching is not possible, consider disabling IPv6 on critical systems

Patch Information

FreeBSD has released security patches addressing this vulnerability in the following versions:

• FreeBSD 12.1-STABLE: r359565 and later
• FreeBSD 12.1-RELEASE: p7 and later
• FreeBSD 11.4-STABLE: r362975 and later
• FreeBSD 11.4-RELEASE: p1 and later
• FreeBSD 11.3-RELEASE: p11 and later

The official security advisory is available at the FreeBSD Security Advisory. Systems using NetApp products built on FreeBSD should also consult the NetApp Security Advisory.

Workarounds

• Disable IPv6 on systems where it is not required by setting ipv6_enable="NO" in /etc/rc.conf
• Limit local user access to prevent untrusted code execution on vulnerable systems
• Implement application sandboxing to restrict socket creation capabilities for untrusted processes
• Use security modules like MAC frameworks to restrict access to sensitive socket operations

# Disable IPv6 on FreeBSD as a temporary workaround
# Add to /etc/rc.conf:
ipv6_enable="NO"

# For immediate effect without reboot (not persistent):
sysctl net.inet6.ip6.v6only=1

# Verify FreeBSD version and patch level
freebsd-version -k