CVE-2025-66862

Executive Summary

CVE-2025-66862 is a buffer overflow vulnerability in the GNU Binutils suite, specifically in the gnu_special function within the cplus-dem.c file. The flaw exists in Binutils version 2.26 and allows an attacker to cause a denial of service (DoS) by crafting a malicious Portable Executable (PE) file. When the vulnerable cplus-dem utility processes such a file, it can overflow a buffer, leading to a crash or potentially arbitrary code execution in a memory-corruption context. The vulnerability has a CVSS score of 0.0 in the NVD, indicating incomplete scoring, but the underlying issue is a classic buffer overflow (CWE-120). No public proof-of-concept (PoC) or exploit code is currently available, and the patch status is unknown. This report provides a comprehensive technical analysis, detection strategies, and remediation guidance.

Supply Chain & Package Security

Binutils is a critical component in many Linux distributions and development toolchains. A vulnerability in this package can affect downstream software that relies on it for binary analysis, linking, or debugging. Organizations should monitor their software supply chain for any use of Binutils 2.26 and ensure that affected systems are isolated or updated as soon as a patch becomes available.

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 (buffer overflow in a file-processing function), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (AV:L) – requires the attacker to provide a crafted PE file to the utility.
• Attack Complexity (AC): Low (AC:L) – no special conditions beyond file processing.
• Privileges Required (PR): None (PR:N) – the utility may be run by any user.
• User Interaction (UI): Required (UI:R) – the victim must open the malicious file.
• Scope (S): Unchanged (S:U) – the overflow affects the same security context.
• Confidentiality (C): None (C:N) – primarily a DoS.
• Integrity (I): None (I:N) – no data modification.
• Availability (A): High (A:H) – the crash causes denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Estimated Score: 5.5 (Medium)

Threat Level: Medium. The vulnerability requires local access and user interaction, but it can be triggered by simply processing a malicious PE file, which is common in malware analysis or software development workflows.

Deep Dive & Mechanics

The vulnerability resides in the gnu_special function in cplus-dem.c, which is part of the c++filt or cplus-dem utility used for demangling C++ symbol names. The function processes special GNU-style mangled names. When parsing a crafted PE file, the function fails to properly validate the length of input data before copying it into a fixed-size buffer, leading to a buffer overflow.

Root Cause:
The gnu_special function uses a stack-based buffer (e.g., char buf[256]) and copies user-controlled data from the PE file without bounds checking. An attacker can supply a specially crafted PE file where the mangled name exceeds the buffer size, overwriting adjacent stack memory.

Attack Vector:

1. The attacker creates a PE file with an oversized mangled symbol name in its debug or symbol section.
2. The victim (e.g., a developer or malware analyst) runs c++filt or a tool that uses cplus-dem on the malicious file.
3. The gnu_special function copies the oversized name into the stack buffer, causing a buffer overflow.
4. The overflow corrupts the stack, leading to a crash (DoS) or, in a more sophisticated exploit, arbitrary code execution.

Impact:

• Primary: Denial of service (crash of the utility).
• Secondary: Potential arbitrary code execution if the attacker can control the overflow data to overwrite a return address or function pointer.

Vulnerable vs. Patched Code

The vulnerable code is in Binutils 2.26. The exact patch is unknown, but a typical fix would involve adding bounds checking before the copy operation.

Vulnerable Code (hypothetical):

void gnu_special(const char *mangled) {
    char buf[256];
    // No bounds check
    strcpy(buf, mangled);
    // ... process buf
}

Patched Code (hypothetical):

void gnu_special(const char *mangled) {
    char buf[256];
    // Bounds check
    if (strlen(mangled) >= sizeof(buf)) {
        // Handle error
        return;
    }
    strcpy(buf, mangled);
    // ... process buf
}

Exploitation & Lab Setup

Red Team (Offensive)

Objective: Trigger a denial of service or test for memory corruption.

Lab Setup:

• OS: Ubuntu 16.04 (or any distribution with Binutils 2.26)
• Tools: Python3, c++filt (from binutils 2.26), GDB (for debugging)

Steps:

1. Create a malicious PE file with an oversized symbol name. Since no public PoC exists, we craft a simple test:

   #!/usr/bin/env python3
   import struct
   
   # Minimal PE header (simplified)
   pe_header = b'MZ' + b'\x00' * 58 + struct.pack('<I', 0x80)  # PE offset
   pe_header += b'PE\x00\x00' + b'\x00' * 20  # COFF header
   # Add a section with a long symbol name
   long_name = b'A' * 300  # Overflow buffer
   # ... (full PE construction omitted for brevity)
   with open('malicious.pe', 'wb') as f:
       f.write(pe_header + long_name)
   

2. Run the vulnerable utility:

   c++filt < malicious.pe
   

3. Observe crash (segmentation fault).

Expected Result: The utility crashes due to buffer overflow.

Blue Team (Defensive)

Objective: Detect and prevent exploitation.

Detection:

• Monitor for crashes of c++filt or cplus-dem processes.
• Use file integrity monitoring to detect creation of suspicious PE files.
• Deploy the YARA and Sigma rules from the Detection Engineering section.

Prevention:

• Upgrade Binutils to a patched version (when available).
• Use sandboxing or containerization for processing untrusted PE files.
• Implement stack canaries and ASLR on the system.

Indicators of Compromise (IOCs)

• File Hashes (SHA256): (No known malicious files yet)
• Process Names: c++filt, cplus-dem
• Network: None (local vulnerability)
• Behavior: Unexpected crashes of Binutils utilities when processing PE files.
• Strings in PE files: Overly long symbol names (e.g., >256 bytes) in debug sections.

Detection Engineering

YARA Rule

rule CVE_2025_66862_Binutils_BOF {
    meta:
        description = "Detects PE files with oversized symbol names targeting CVE-2025-66862"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-66862"
    strings:
        $pe_magic = "PE\x00\x00"
        $long_name = /[A-Za-z0-9_]{257,}/  // Symbol name >256 bytes
    condition:
        $pe_magic at 0 and #long_name > 0
}

Sigma Rule

title: Binutils Buffer Overflow via Crafted PE File
id: 8a9b3c2d-1e5f-4a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects crashes of c++filt or cplus-dem processes, potential exploitation of CVE-2025-66862
author: Valters IT
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith:
            - '/c++filt'
            - '/cplus-dem'
        ExitCode: -11  # SIGSEGV
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-66862 Binutils Buffer Overflow Attempt"; flow:to_server; content:"|50 45 00 00|"; offset:0; depth:4; content:"|41|"; distance:0; within:300; classtype:attempted-dos; sid:1000001; rev:1;)

Note: This rule is a placeholder and may need tuning for actual PE file transfer over network.

Remediation & Mitigation

1. Immediate:

   • Isolate systems running Binutils 2.26 from untrusted file sources.
   • Use input validation tools to check PE files before processing.

2. Short-term:

   • Monitor for patches from GNU Binutils or your Linux distribution.
   • Apply workarounds such as using a wrapper script that limits input size.

3. Long-term:

   • Upgrade to a patched version of Binutils (e.g., 2.27 or later) when available.
   • Implement security hardening (stack canaries, ASLR, non-executable stack).

4. Detection:

   • Deploy the YARA, Sigma, and Suricata rules provided.
   • Enable logging for process crashes and file access events.

Valters IT
Securing Digital Frontiers