CVE-2025-6272

Executive Summary

CVE-2025-6272 is a locally exploitable out-of-bounds write vulnerability in Wasm3 version 0.5.0, specifically within the MarkSlotAllocated function in source/m3_compile.c. The vulnerability allows an attacker to trigger a write beyond the allocated memory bounds, potentially leading to a denial of service or memory corruption. With a CVSS score of 3.3 (Low), the risk is limited due to the requirement for local access and the low impact on confidentiality and integrity. However, the public availability of exploit details increases the urgency for mitigation.

Supply Chain & Package Security

Wasm3 is a WebAssembly interpreter used in various embedded and edge computing environments. While not a direct package manager dependency (like NPM or PyPI), its integration into larger systems can introduce supply chain risks. Organizations using Wasm3 in their software stack should verify the version and apply any available patches or workarounds.

CVSS Breakdown & Threat Level

• CVSS Score: 3.3 (Low)
• Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Attack Vector: Local (AV:L) – Requires physical or logical access to the system.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Vulnerability does not affect other components.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: Low (A:L) – Potential for denial of service.

Threat Level: Low. The requirement for local access significantly reduces the attack surface. However, in environments where untrusted code can be executed locally (e.g., sandboxed applications), the risk increases.

Deep Dive & Mechanics

The vulnerability resides in the MarkSlotAllocated function within source/m3_compile.c. This function is responsible for marking a slot in a memory region as allocated during WebAssembly bytecode compilation. The out-of-bounds write occurs when the function writes to an index that exceeds the allocated buffer size, likely due to insufficient bounds checking on the slot index.

Technical Details:

• Function: MarkSlotAllocated
• File: source/m3_compile.c
• Root Cause: Lack of validation on the slot index before writing to the memory buffer.
• Trigger: Compilation of a crafted WebAssembly module that specifies an out-of-bounds slot index.
• Impact: Memory corruption, potentially leading to a crash or exploitable conditions.

The exploit is publicly disclosed, meaning attackers have access to the technical details needed to reproduce the issue.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code is present in Wasm3 version 0.5.0. The following is a conceptual comparison:

Vulnerable Code (source/m3_compile.c):

void MarkSlotAllocated(M3Compilation *comp, int slot) {
    // No bounds check on slot
    comp->slot_allocated[slot] = 1;
}

Patched Code (hypothetical):

void MarkSlotAllocated(M3Compilation *comp, int slot) {
    if (slot < 0 || slot >= MAX_SLOTS) {
        // Handle error or return
        return;
    }
    comp->slot_allocated[slot] = 1;
}

The patch would add a bounds check to ensure the slot index is within the valid range before writing.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a system running Wasm3 0.5.0.
• Ability to provide a crafted WebAssembly module to the interpreter.

Exploitation Steps:

1. Craft a Malicious WebAssembly Module: Create a .wasm file that triggers the out-of-bounds write during compilation. The module should specify a slot index larger than the allocated buffer.
2. Execute the Module: Run the module using Wasm3:

   wasm3 malicious.wasm
   

3. Observe Crash: The interpreter may crash due to memory corruption, or the attacker may achieve controlled memory write if the environment allows.

Proof of Concept (Conceptual):

(module
  (func (export "trigger") (result i32)
    i32.const 9999  ;; Out-of-bounds slot index
    drop
    i32.const 0
  )
)

Blue Team

Detection:

• Monitor for crashes or abnormal terminations of Wasm3 processes.
• Use memory integrity checks (e.g., AddressSanitizer) during development.

Mitigation:

• Restrict local execution of untrusted WebAssembly modules.
• Apply memory protection mechanisms (e.g., ASLR, DEP).
• Monitor for known exploit signatures.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (None provided; generate upon exploit discovery)
• Process Names: wasm3
• Log Entries: Segmentation faults or memory access violations in system logs.
• Network Indicators: None (local vulnerability).
• Behavioral: Unexpected crashes of Wasm3 when processing WebAssembly modules.

Detection Engineering

YARA Rule

rule CVE_2025_6272_Wasm3_OOB_Write {
    meta:
        description = "Detects Wasm3 binary with vulnerable MarkSlotAllocated function"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-6272"
    strings:
        $vuln_func = "MarkSlotAllocated"
        $vuln_code = { 8B ?? ?? 83 ?? ?? 01 }  // Example opcode pattern for out-of-bounds write
    condition:
        $vuln_func and $vuln_code
}

Sigma Rule

title: Wasm3 Out-of-Bounds Write Exploitation Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects potential exploitation of CVE-2025-6272 via crash or memory access violation
author: Valters IT
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/wasm3'
        CommandLine|contains: '.wasm'
    condition: selection
falsepositives:
    - Legitimate use of Wasm3 with normal modules
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-6272 Wasm3 Out-of-Bounds Write Attempt"; flow:to_server; content:"|00 61 73 6d|"; depth:4; content:"|01 00 00 00|"; distance:4; within:4; reference:cve,2025-6272; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict Access: Limit local execution of Wasm3 to trusted users only.
2. Monitor Logs: Watch for crashes or abnormal behavior in Wasm3 processes.
3. Apply Workarounds: If possible, use a different WebAssembly interpreter or sandbox Wasm3 execution.

Long-Term Fix:

• Await an official patch from the Wasm3 maintainers. In the meantime, consider forking the repository and applying the bounds check manually.

Compensating Controls:

• Use memory-safe languages or tools (e.g., Rust, AddressSanitizer) for WebAssembly interpretation.
• Implement strict input validation for WebAssembly modules.

Valters IT
Securing Digital Frontiers