CVE-2023-50559

Executive Summary

CVE-2023-50559 is a vulnerability in the XiangShan v2.1 processor that allows local attackers to obtain sensitive information via the L1D cache. The vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The CVSS score is 0.0, indicating insufficient data for scoring, but the nature of the issue suggests a potential side-channel attack vector. No public proof-of-concept (PoC) or patch details are currently available. The EPSS score is 0.0%, indicating low exploitation probability in the wild.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unscored)
• Attack Vector: Local (AV:L)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: None (I:N)
• Availability Impact: None (A:N)
• Threat Level: Medium (due to local access requirement but potential for sensitive data leakage)

Deep Dive & Mechanics

The vulnerability resides in the L1D cache of the XiangShan v2.1 processor, an open-source RISC-V core. The issue allows a local attacker to infer sensitive information by observing cache timing or access patterns. This is a classic side-channel attack, similar to Flush+Reload or Prime+Probe techniques, where an attacker can monitor cache line evictions or accesses to deduce secret data (e.g., cryptographic keys). The attack requires local code execution on the same core, making it relevant for multi-tenant environments or sandboxed applications.

Vulnerable vs. Patched Code

No patch details are available. The vulnerable component is the L1D cache controller in XiangShan v2.1. Without a patch, the code remains susceptible to side-channel leakage. A potential fix would involve implementing cache partitioning, randomization, or constant-time memory access patterns to mitigate timing differences.

Exploitation & Lab Setup

Red Team

• Prerequisites: Local user access on a system with XiangShan v2.1 processor.
• Exploit Technique: Use a Flush+Reload or Prime+Probe side-channel attack to monitor L1D cache lines.
• Lab Setup:
  1. Set up a QEMU emulation of XiangShan v2.1 or use a physical FPGA board.
  2. Write a victim process that accesses sensitive data (e.g., AES key schedule).
  3. Write an attacker process that flushes and probes cache lines to detect access patterns.
• Example Code Snippet (Flush+Reload):

  // Attacker flushes a shared memory line
  _mm_clflush(addr);
  // Victim accesses the line
  // Attacker reloads and measures time
  start = rdtsc();
  temp = *addr;
  end = rdtsc();
  if (end - start < THRESHOLD) {
      // Victim accessed the line
  }
  

Blue Team

• Detection: Monitor for high-frequency cache flush instructions (e.g., clflush) or abnormal timing measurements.
• Mitigation: Disable hyper-threading, use cache partitioning, or implement constant-time algorithms.
• Lab Setup: Use performance counters to detect cache side-channel attacks.

Indicators of Compromise (IOCs)

• Cache Timing Anomalies: Unusual patterns in L1D cache miss/hit ratios.
• High Rate of clflush Instructions: Excessive cache line flushes from a user-space process.
• Performance Counter Spikes: Elevated values for L1D_CACHE_MISS or L1D_CACHE_ACCESS events.

Detection Engineering

YARA Rule

rule CVE_2023_50559_Cache_Attack {
    meta:
        description = "Detects potential L1D cache side-channel attack code"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $clflush = { 0F AE 38 }  // clflush [rax] or similar
        $rdtsc = { 0F 31 }       // rdtsc
        $mfence = { 0F AE F0 }   // mfence
    condition:
        any of them
}

Sigma Rule

title: Cache Side-Channel Attack Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects frequent cache flush instructions indicative of side-channel attacks
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/victim_process'
        CommandLine|contains: 'clflush'
    condition: selection
falsepositives:
    - Legitimate cache maintenance operations
level: medium

Suricata Rule

alert ip any any -> any any (msg:"CVE-2023-50559 Cache Side-Channel Attempt"; content:"|0F AE 38|"; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Disable hyper-threading on affected systems.
• Short-term: Implement cache partitioning or randomization in the processor design.
• Long-term: Apply constant-time programming practices for sensitive operations.
• Workaround: Use software-based mitigations like cache flushing after sensitive operations.

Valters IT
DevSecOps & Cyber Threat Intelligence