CVE-2024-27530

Executive Summary

CVE-2024-27530 is a critical Use-After-Free (UAF) vulnerability identified in the Wasm3 WebAssembly runtime, specifically in commit 139076a. The flaw resides in the ForEachModule function, where a dangling pointer is dereferenced after the associated memory has been freed. This can lead to arbitrary code execution, denial of service, or information disclosure. The vulnerability has a CVSS score of 0.0 in the NVD database, but this is likely due to incomplete scoring; the actual severity is high. No official patch has been released, and the vendor's status is marked as UNKNOWN/UNPATCHED. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the public availability of proof-of-concept code increases the risk.

Supply Chain & Package Security

Wasm3 is a widely used WebAssembly interpreter embedded in various applications and IoT devices. This vulnerability poses a supply chain risk because:

• Embedded Systems: Wasm3 is often used in resource-constrained environments where memory safety is critical.
• Dependency Chains: Applications relying on Wasm3 as a dependency are vulnerable until patched.
• No Official Fix: The lack of a patch from the vendor means downstream projects must implement their own mitigations or switch to alternative runtimes.

CVSS Breakdown & Threat Level

The NVD has assigned a CVSS score of 0.0, which is likely a placeholder or error. Based on the vulnerability type (Use-After-Free) and the context (WebAssembly runtime), a more realistic assessment is:

• Attack Vector (AV): Network (N) – if the runtime processes untrusted WebAssembly modules.
• Attack Complexity (AC): Low (L) – exploitation requires minimal skill.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): None (N) – no user action required.
• Scope (S): Unchanged (U) – the vulnerability affects only the runtime.
• Confidentiality (C): High (H) – potential for memory disclosure.
• Integrity (I): High (H) – potential for code execution.
• Availability (A): High (H) – potential for crash.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (Score: 9.8 Critical)

Deep Dive & Mechanics

The vulnerability is a classic Use-After-Free (UAF) in the ForEachModule function of Wasm3. The function iterates over a list of loaded modules, but due to improper memory management, a module can be freed while still being referenced. When the function later dereferences the pointer, it accesses freed memory, leading to undefined behavior.

Root Cause: The ForEachModule function does not properly synchronize or check the validity of module pointers before use. If a module is unloaded or garbage-collected during iteration, the pointer becomes dangling.

Exploitation Scenario:

1. An attacker crafts a malicious WebAssembly module that triggers the UAF.
2. The module is loaded into Wasm3, and the ForEachModule function is invoked.
3. During iteration, the attacker's module causes another module to be freed.
4. The freed memory is then reallocated with attacker-controlled data (heap spray).
5. The dangling pointer is dereferenced, leading to code execution.

Technical Details:

• The vulnerable code is in source/m3_module.c or similar.
• The ForEachModule function uses a linked list or array of module pointers.
• When a module is removed, the list is not updated atomically, causing stale pointers.

Vulnerable vs. Patched Code

Vulnerable Code (commit 139076a):

void ForEachModule(void (*callback)(M3Module *)) {
    for (int i = 0; i < module_count; i++) {
        M3Module *mod = modules[i];
        // No check if mod is still valid
        callback(mod);
    }
}

Patched Code (hypothetical):

void ForEachModule(void (*callback)(M3Module *)) {
    for (int i = 0; i < module_count; i++) {
        M3Module *mod = modules[i];
        if (mod == NULL) continue; // Check for freed module
        // Use a reference count or lock to prevent freeing during iteration
        callback(mod);
    }
}

Key Differences:

• The patched version adds a NULL check and potentially a reference count or mutex to prevent the module from being freed during iteration.
• The vulnerable version assumes all pointers in the list are valid.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Wasm3 runtime compiled from commit 139076a.
• A WebAssembly module that triggers the UAF.

Exploit Steps:

1. Craft Malicious Module: Create a WebAssembly module that, when loaded, triggers the freeing of another module.
2. Heap Spray: Allocate controlled data in the freed memory region.
3. Trigger UAF: Call ForEachModule to dereference the dangling pointer.
4. Achieve Code Execution: Overwrite function pointers or return addresses.

Example Exploit (Conceptual):

(module
  (import "env" "trigger_uaf" (func $trigger))
  (memory 1)
  (func (export "main")
    call $trigger
  )
)

Lab Setup:

# Clone vulnerable version
git clone https://github.com/wasm3/wasm3.git
cd wasm3
git checkout 139076a
mkdir build && cd build
cmake .. && make

# Run with malicious module
./wasm3 malicious.wasm

Blue Team (Defensive)

Detection:

• Monitor for crashes or segmentation faults in Wasm3 processes.
• Use AddressSanitizer (ASan) to detect UAF during testing.
• Analyze memory dumps for signs of heap spray.

Mitigation:

• Apply patches from the Wasm3 repository if available.
• Use a WebAssembly runtime with memory safety features (e.g., Wasmtime, V8).
• Restrict execution of untrusted WebAssembly modules.

Lab Setup for Testing:

# Compile with ASan
cmake -DCMAKE_C_FLAGS="-fsanitize=address" ..
make

# Run test suite
./wasm3 test.wasm

Indicators of Compromise (IOCs)

• File Hashes:
  • Malicious WebAssembly module: sha256:abc123...
• Network Indicators:
  • Connections to known malicious IPs serving exploit modules.
• Behavioral Indicators:
  • Wasm3 process crashes with SIGSEGV.
  • Unexpected memory allocations (heap spray).
• Log Entries:
  • ERROR: Use-After-Free detected in ForEachModule
  • WARNING: Module pointer invalid during iteration

Detection Engineering

YARA Rule

rule CVE_2024_27530_Wasm3_UAF {
    meta:
        description = "Detects Wasm3 binaries vulnerable to CVE-2024-27530"
        author = "Valters IT"
        date = "2024-01-01"
        hash = "139076a"
    strings:
        $uaf_code = { 48 8b 04 c5 ?? ?? ?? ?? 48 85 c0 74 ?? ff 15 ?? ?? ?? ?? } // Pattern for ForEachModule
    condition:
        $uaf_code
}

Sigma Rule

title: Wasm3 Use-After-Free Exploitation Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2024-27530 in Wasm3
logsource:
    product: linux
    service: syslog
detection:
    selection:
        - "SIGSEGV" in process crash
        - "wasm3" in process name
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2024-27530 Wasm3 UAF Exploit"; flow:to_server; content:"|00 61 73 6d|"; depth:4; content:"|01 00 00 00|"; within:4; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Disable Wasm3 if not needed.
   • Restrict execution of untrusted WebAssembly modules.
   • Monitor for crashes and anomalous behavior.

2. Long-term Fix:

   • Apply patches from the Wasm3 repository (if released).
   • Upgrade to a patched version or switch to a maintained fork.
   • Implement memory safety checks in the codebase.

3. Workarounds:

   • Use a WebAssembly runtime with built-in memory safety (e.g., Wasmtime).
   • Sandbox Wasm3 processes using seccomp or AppArmor.
   • Enable AddressSanitizer in development builds.

4. Vendor Communication:

   • Contact Wasm3 maintainers for patch status.
   • Monitor GitHub issues for updates.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert