CVE-2023-0458: Linux Kernel Information Disclosure Flaw

CVE-2023-0458 Overview

A speculative pointer dereference vulnerability exists in the Linux Kernel's do_prlimit() function. The resource argument value is controlled by the attacker and used in pointer arithmetic for the rlim variable, which can be exploited to leak kernel memory contents through speculative execution side-channels. This vulnerability is classified as an information disclosure issue that could allow local attackers with low privileges to extract sensitive data from kernel memory.

Critical Impact

Local attackers can potentially leak sensitive kernel memory contents by exploiting speculative execution in the do_prlimit() function, bypassing traditional memory isolation protections.

Affected Products

• Linux Kernel versions prior to 6.1.8
• Linux Kernel 6.2 RC1 through RC4
• Debian Linux 10.0

Discovery Timeline

• 2023-04-26 - CVE-2023-0458 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-0458

Vulnerability Analysis

This vulnerability stems from a speculative pointer dereference in the Linux Kernel's resource limit handling code. The do_prlimit() function in kernel/sys.c processes resource limit requests without adequate speculation barriers. When an attacker controls the resource parameter, they can manipulate pointer arithmetic operations to access out-of-bounds memory locations during speculative execution, potentially leaking sensitive kernel data through cache timing side-channels similar to Spectre-class vulnerabilities.

The vulnerability requires local access to the system and the attacker must have low-level privileges to invoke the affected system call. The complexity of exploitation is high as it requires precise timing and understanding of speculative execution behavior.

Root Cause

The root cause is the absence of speculation barriers in the do_prlimit() function when processing user-controlled resource values. The function performs bounds checking (if (resource >= RLIM_NLIMITS) return -EINVAL;) but does not prevent speculative execution from proceeding with out-of-bounds values before the check completes. This allows the CPU to speculatively access memory using attacker-controlled indices, leaving observable traces in the cache that can be measured to infer memory contents.

Attack Vector

The attack vector is local, requiring the attacker to have code execution on the target system. The attacker invokes the prlimit() or prlimit64() system call with a carefully crafted resource value. While the kernel will ultimately reject invalid resource values, speculative execution may temporarily access memory at attacker-controlled offsets. By measuring cache timing differences, the attacker can infer the contents of kernel memory that was speculatively accessed.

The following patch was applied to address the vulnerability:

 
 	if (resource >= RLIM_NLIMITS)
 		return -EINVAL;
+	resource = array_index_nospec(resource, RLIM_NLIMITS);
+
 	if (new_rlim) {
 		if (new_rlim->rlim_cur > new_rlim->rlim_max)
 			return -EINVAL;

Source: GitHub Linux Commit

The fix adds array_index_nospec() which sanitizes the resource index to prevent speculative out-of-bounds access, ensuring the bounds check is enforced before any memory access occurs.

Detection Methods for CVE-2023-0458

Indicators of Compromise

• Unusual patterns of prlimit() or prlimit64() system calls with invalid or boundary-value resource parameters
• Processes performing high-frequency calls to resource limit functions combined with precision timing measurements
• Suspicious processes accessing /proc filesystem entries related to resource limits in abnormal patterns

Detection Strategies

• Monitor for anomalous system call patterns using audit frameworks like auditd to track prlimit64 syscalls with unusual arguments
• Deploy kernel-level monitoring to detect processes attempting to probe cache timing differences
• Utilize SentinelOne's behavioral AI to identify exploitation patterns characteristic of Spectre-class attacks

Monitoring Recommendations

• Enable kernel auditing for resource limit system calls with filters for edge-case resource values
• Implement host-based intrusion detection rules to flag processes exhibiting cache timing attack behaviors
• Review system logs for repeated failed prlimit calls that may indicate exploitation attempts

How to Mitigate CVE-2023-0458

Immediate Actions Required

• Upgrade the Linux Kernel to version 6.1.8 or later which contains the security fix
• Apply commit 739790605705ddcf18f21782b9c99ad7d53a8c11 if using a custom kernel build
• For Debian Linux 10.0 users, apply the latest security updates as per the Debian LTS advisories

Patch Information

The vulnerability has been addressed in Linux Kernel version 6.1.8 and subsequent releases. The fix introduces the array_index_nospec() macro call to prevent speculative execution from using attacker-controlled index values. Vendor advisories and patches are available:

• Linux Kernel Diff Changes - Official kernel patch diff
• GitHub Linux Commit - Security commit details
• Debian LTS Advisory - Debian security announcement

Workarounds

• Restrict local access to trusted users only, as the vulnerability requires local code execution
• Implement strict process isolation using containers or VMs to limit the impact of potential information leakage
• Consider enabling additional Spectre mitigations in kernel boot parameters if immediate patching is not possible

# Check current kernel version
uname -r

# Update kernel on Debian-based systems
sudo apt update && sudo apt upgrade linux-image-$(uname -r)

# Verify the patch is applied by checking kernel version is >= 6.1.8