CVE-2023-28772: Linux Kernel Buffer Overflow Vulnerability

CVE-2023-28772 Overview

CVE-2023-28772 is a buffer overflow vulnerability discovered in the Linux kernel's lib/seq_buf.c implementation. The vulnerability specifically affects the seq_buf_putmem_hex() function, which improperly handles buffer boundaries when converting memory contents to hexadecimal representation. This flaw exists in Linux kernel versions prior to 5.13.3 and could allow a local attacker with elevated privileges to potentially achieve code execution or cause system instability through memory corruption.

Critical Impact

Local attackers with high privileges can exploit this buffer overflow in seq_buf_putmem_hex() to corrupt memory, potentially leading to privilege escalation, arbitrary code execution, or system crashes affecting kernel stability.

Affected Products

• Linux Kernel versions prior to 5.13.3
• Systems running vulnerable kernel versions across all supported architectures
• NetApp products using affected Linux kernel versions (see NetApp Security Advisory)

Discovery Timeline

• 2023-03-23 - CVE-2023-28772 published to NVD
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2023-28772

Vulnerability Analysis

The buffer overflow in seq_buf_putmem_hex() occurs due to incorrect calculation of the buffer size needed for hexadecimal conversion operations. The function is designed to convert raw memory bytes into their hexadecimal string representation for debugging and tracing purposes. However, the original implementation failed to properly account for the fact that each byte of memory requires two hexadecimal characters for representation, leading to potential buffer boundary violations.

The vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input), indicating a classic buffer overflow pattern where data is copied into a fixed-size buffer without adequate bounds checking. This type of flaw in kernel code is particularly concerning as it operates in the most privileged execution context.

Root Cause

The root cause lies in the seq_buf_putmem_hex() function's handling of the start_len calculation. The original code used HEX_CHARS - 1 as the maximum length for processing, but this value was too large considering that each byte converts to two hexadecimal characters. The fix introduces MAX_MEMHEX_BYTES as a proper boundary and adds a compile-time assertion (BUILD_BUG_ON) to ensure that MAX_MEMHEX_BYTES * 2 is always less than HEX_CHARS, preventing any future regressions.

Attack Vector

This vulnerability requires local access to the system and elevated privileges to exploit. An attacker would need to trigger the seq_buf_putmem_hex() function with carefully crafted input that exceeds the expected buffer boundaries. The attack surface includes kernel tracing facilities, debugging interfaces, and any kernel subsystem that utilizes the seq_buf library for hexadecimal memory dumps. While the local attack vector and high privilege requirement limit exposure, successful exploitation could result in kernel memory corruption with potential for privilege escalation or arbitrary code execution.

// Security patch from lib/seq_buf.c - Source: GitHub kernel commit
 
	WARN_ON(s->size == 0);
 
+	BUILD_BUG_ON(MAX_MEMHEX_BYTES * 2 >= HEX_CHARS);
+
	while (len) {
-		start_len = min(len, HEX_CHARS - 1);
+		start_len = min(len, MAX_MEMHEX_BYTES);
 #ifdef __BIG_ENDIAN
		for (i = 0, j = 0; i < start_len; i++) {
 #else

Source: GitHub Commit by Linus Torvalds

Detection Methods for CVE-2023-28772

Indicators of Compromise

• Unexpected kernel panics or system crashes related to seq_buf operations
• Anomalous memory access patterns in kernel debugging or tracing subsystems
• Kernel log entries indicating buffer overflows or memory corruption in lib/seq_buf.c
• Unusual behavior in ftrace, printk, or other kernel tracing facilities

Detection Strategies

• Monitor kernel version using uname -r and compare against the fixed version 5.13.3
• Deploy kernel integrity monitoring solutions to detect unauthorized kernel memory modifications
• Implement system call auditing to track privileged operations that may trigger vulnerable code paths
• Use SentinelOne's kernel-level monitoring capabilities to detect anomalous kernel behavior patterns

Monitoring Recommendations

• Enable kernel auditing for tracing-related system calls and operations
• Configure alerting on unexpected kernel oops or panic events
• Monitor for processes attempting to access kernel debugging interfaces with suspicious patterns
• Deploy endpoint detection solutions capable of monitoring kernel-level activity

How to Mitigate CVE-2023-28772

Immediate Actions Required

• Update Linux kernel to version 5.13.3 or later immediately
• Review and restrict access to kernel debugging and tracing interfaces
• Limit local user privileges to reduce the attack surface for exploitation
• Apply vendor-specific patches from distribution maintainers (RHEL, Ubuntu, Debian, etc.)

Patch Information

The vulnerability was addressed in Linux kernel version 5.13.3. The fix modifies the seq_buf_putmem_hex() function in lib/seq_buf.c to use a correctly sized constant (MAX_MEMHEX_BYTES) and adds a compile-time check to prevent buffer overflow conditions. The patch is available through the official Linux kernel repository and has been backported to various distribution kernels.

For detailed patch information, refer to the Linux Kernel ChangeLog 5.13.3 and the GitHub commit.

Workarounds

• Restrict access to kernel tracing interfaces using appropriate access controls
• Disable unnecessary kernel debugging features in production environments
• Implement strict privilege separation to limit accounts with kernel-level access
• Use security modules (SELinux, AppArmor) to confine processes that interact with kernel tracing

# Check current kernel version
uname -r

# Verify if system is vulnerable (versions below 5.13.3 are affected)
# Update kernel using package manager (example for Debian/Ubuntu)
sudo apt update && sudo apt upgrade linux-image-generic

# Restrict access to kernel tracing interfaces
sudo chmod 700 /sys/kernel/debug/tracing