CVE-2022-27666: Linux Kernel Privilege Escalation Flaw

CVE-2022-27666 Overview

A heap buffer overflow vulnerability was discovered in the Linux kernel's IPsec Encapsulating Security Payload (ESP) transformation code. The flaw exists in net/ipv4/esp4.c and net/ipv6/esp6.c, which handle ESP packet processing for IPv4 and IPv6 respectively. This vulnerability allows a local attacker with normal user privileges to overwrite kernel heap objects, potentially leading to local privilege escalation.

Critical Impact

Local attackers can exploit this heap buffer overflow to corrupt kernel memory structures and escalate privileges from a standard user account to root access, compromising system integrity entirely.

Affected Products

• Linux Kernel (versions prior to 5.17 and including 5.17-rc1 through 5.17-rc7)
• Fedora 34 and 35
• Red Hat Enterprise Linux 8.0
• Red Hat Virtualization 4.0
• Debian Linux 9.0, 10.0, and 11.0
• NetApp H-Series Storage Systems (H300S, H500S, H700S, H300E, H500E, H700E, H410S, H410C)

Discovery Timeline

• 2022-03-23 - CVE-2022-27666 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-27666

Vulnerability Analysis

This heap buffer overflow vulnerability (CWE-787: Out-of-bounds Write) occurs in the ESP transformation code within the Linux kernel's IPsec implementation. The flaw stems from improper allocation size calculations when processing ESP packets, allowing memory writes beyond the intended buffer boundaries.

The vulnerability requires local access to the system, meaning an attacker must have an existing user account on the target machine. Once exploited, the attacker can overwrite adjacent kernel heap objects, which can be leveraged to gain elevated privileges. The impact is severe as successful exploitation grants the attacker full control over kernel memory, potentially leading to complete system compromise with root-level access.

Root Cause

The root cause lies in insufficient bounds checking during ESP packet transformation. The code failed to properly constrain the maximum fragment size when allocating memory for ESP operations. Without the ESP_SKB_FRAG_MAXSIZE definition limiting the allocation size, an attacker could craft malicious input that triggers a heap overflow condition when the kernel processes ESP-encrypted packets.

Attack Vector

The attack vector is local, requiring the attacker to have a valid user account on the target system. The attacker can trigger the vulnerability by:

1. Crafting specially formatted IPsec ESP packets with oversized payloads
2. Sending these packets through the kernel's ESP transformation layer
3. Causing the kernel to write beyond allocated heap buffer boundaries
4. Manipulating adjacent heap objects to achieve code execution or privilege escalation

The low attack complexity and no user interaction requirement make this vulnerability particularly dangerous in multi-user environments.

// Security patch in include/net/esp.h
// Source: https://github.com/torvalds/linux/commit/ebe48d368e97d007bfeb76fcb065d6cfc4c96645
 
 #include <linux/skbuff.h>
 
+#define ESP_SKB_FRAG_MAXSIZE (PAGE_SIZE << SKB_FRAG_PAGE_ORDER)
+
 struct ip_esp_hdr;
 
 static inline struct ip_esp_hdr *ip_esp_hdr(const struct sk_buff *skb)

The patch introduces ESP_SKB_FRAG_MAXSIZE to constrain the maximum allocation size for ESP fragments, preventing the overflow condition.

// Security patch in net/ipv4/esp4.c
// Source: https://github.com/torvalds/linux/commit/ebe48d368e97d007bfeb76fcb065d6cfc4c96645
 	struct page *page;
 	struct sk_buff *trailer;
 	int tailen = esp->tailen;
+	unsigned int allocsz;
 
 	/* this is non-NULL only with TCP/UDP Encapsulation */
 	if (x->encap) {

This patch adds the allocsz variable to properly track and constrain allocation sizes during ESP packet processing.

Detection Methods for CVE-2022-27666

Indicators of Compromise

• Unusual kernel panic or system crashes related to IPsec/ESP processing
• Unexpected privilege escalation events from low-privileged user accounts
• Anomalous memory allocation patterns in kernel logs related to esp4.c or esp6.c
• Process execution by users that shouldn't have elevated capabilities

Detection Strategies

• Monitor kernel logs for memory corruption errors or oops messages referencing ESP transformation functions
• Implement system call auditing to detect unusual IPsec-related socket operations from non-administrative users
• Deploy kernel-level integrity monitoring to detect unauthorized modifications to kernel memory structures
• Use SentinelOne's behavioral AI to identify privilege escalation attempts following network stack operations

Monitoring Recommendations

• Enable kernel auditing for IPsec subsystem operations and socket creation
• Monitor for processes attempting to load or manipulate IPsec security associations
• Track user privilege changes and correlate with preceding IPsec-related system activity
• Implement file integrity monitoring on critical system binaries that could be modified post-exploitation

How to Mitigate CVE-2022-27666

Immediate Actions Required

• Update the Linux kernel to the latest patched version that includes commit ebe48d368e97d007bfeb76fcb065d6cfc4c96645
• Apply vendor-specific security updates from Red Hat, Debian, Fedora, or NetApp as applicable
• Restrict local user access on systems where kernel updates cannot be immediately applied
• Enable kernel address space layout randomization (KASLR) to increase exploitation difficulty

Patch Information

The vulnerability has been addressed in the upstream Linux kernel through commit ebe48d368e97d007bfeb76fcb065d6cfc4c96645. Major distributions have released corresponding security updates:

• Red Hat has tracked this issue via Bug #2061633
• Debian has released fixes in DSA-5127 and DSA-5173
• NetApp has published Advisory NTAP-20220429-0001

Organizations should prioritize kernel updates through their standard patch management processes.

Workarounds

• Disable IPsec functionality if not required for operations until patching is complete
• Implement strict user access controls to limit local access to affected systems
• Use SELinux or AppArmor policies to restrict unprivileged user access to IPsec functionality
• Consider network segmentation to isolate systems that cannot be immediately patched

# Verify current kernel version
uname -r

# Check if IPsec modules are loaded
lsmod | grep esp

# Temporarily unload ESP modules if IPsec is not required (requires root)
# WARNING: Only do this if IPsec/VPN functionality is not needed
modprobe -r esp4
modprobe -r esp6

# Blacklist ESP modules to prevent automatic loading (temporary workaround)
echo "blacklist esp4" >> /etc/modprobe.d/disable-esp.conf
echo "blacklist esp6" >> /etc/modprobe.d/disable-esp.conf