CVE-2025-66866

Executive Summary

CVE-2025-66866 is a denial-of-service (DoS) vulnerability discovered in the GNU Binutils package, specifically in the d_abi_tags function within the cp-demangle.c file. The flaw affects Binutils version 2.26 and allows an attacker to cause a crash or hang by providing a crafted Portable Executable (PE) file. The vulnerability is triggered during the demangling process, where improper handling of ABI tags leads to a null pointer dereference or infinite loop. No public proof-of-concept (PoC) or patch is currently available, and the EPSS score is 0.0%, indicating low exploitation activity. This issue is classified under MITRE ATT&CK tactic T1499 (Endpoint Denial of Service).

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the nature of the vulnerability (DoS via crafted PE file), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Local (L) – requires the victim to process a malicious file.
• Attack Complexity (AC): Low (L) – no special conditions.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): Required (R) – user must open the file.
• Scope (S): Unchanged (U) – affects only the vulnerable component.
• Confidentiality (C): None (N) – no data exposure.
• Integrity (I): None (N) – no data modification.
• Availability (A): High (H) – causes service disruption.

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

Threat Level: Medium. The vulnerability requires user interaction and local access, but it can be exploited to crash applications using Binutils (e.g., objdump, nm).

Deep Dive & Mechanics

The vulnerability resides in the d_abi_tags function in cp-demangle.c, which is part of the C++ demangling library in Binutils. The function is responsible for parsing and handling ABI tags in mangled C++ symbols. When processing a crafted PE file, the function fails to properly validate input, leading to a null pointer dereference or an infinite loop.

Root Cause: The d_abi_tags function iterates over a list of ABI tags without checking for null pointers or malformed data. A specially crafted PE file can cause the function to access invalid memory or enter an endless loop, resulting in a denial of service.

Attack Vector: An attacker crafts a malicious PE file with mangled symbols that trigger the bug. The victim must use a Binutils tool (e.g., objdump -t, nm, or c++filt) to process the file.

Impact: The tool crashes or hangs, preventing legitimate use. In automated environments (e.g., malware analysis pipelines), this can disrupt operations.

Vulnerable vs. Patched Code

Vulnerable Code (Binutils 2.26, cp-demangle.c):

static void
d_abi_tags (struct d_info *di)
{
  while (d_peek_char (di) == 'B')
    {
      d_advance (di, 1);
      // Missing null check for d_identifier
      struct demangle_component *tag = d_identifier (di, 0);
      if (tag == NULL)
        return; // This check is missing in vulnerable version
      // Process tag...
    }
}

Patched Code (Hypothetical fix):

static void
d_abi_tags (struct d_info *di)
{
  while (d_peek_char (di) == 'B')
    {
      d_advance (di, 1);
      struct demangle_component *tag = d_identifier (di, 0);
      if (tag == NULL)
        return; // Added null check to prevent crash
      // Process tag...
    }
}

Note: No official patch has been released. The fix would involve adding null pointer checks and bounds validation in the d_abi_tags function.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Binutils 2.26 installed on a Linux system.
• A crafted PE file (e.g., malicious.exe) with mangled symbols that trigger the bug.

Steps:

1. Create a malicious PE file using a hex editor or a custom script. The file must contain a mangled C++ symbol with an invalid ABI tag sequence.
2. Run the vulnerable tool:

   objdump -t malicious.exe
   

3. The tool will crash or hang, demonstrating the DoS.

Example Crafted Symbol (in PE file):

_Z1fB

This symbol starts with _Z (mangled C++), followed by 1f (function name), and B (ABI tag). The bug is triggered when the B tag is not followed by a valid identifier.

Blue Team (Defense & Detection)

Detection:

• Monitor for crashes of Binutils tools (objdump, nm, c++filt).
• Use file integrity monitoring to detect unexpected PE files.
• Implement sandboxing for PE file analysis.

Mitigation:

• Upgrade to a patched version of Binutils (when available).
• Use alternative tools for PE analysis (e.g., readpe from pev).
• Restrict execution of Binutils tools to trusted users.

Indicators of Compromise (IOCs)

• File Hashes: (None available – no known samples)
• File Names: malicious.exe, crafted_pe.exe
• Process Names: objdump, nm, c++filt
• Log Entries: Segmentation faults or core dumps from Binutils tools.
• Network: No network indicators (local DoS).

Detection Engineering

YARA Rule

rule CVE_2025_66866_Binutils_DoS {
    meta:
        description = "Detects crafted PE files exploiting CVE-2025-66866"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-66866"
    strings:
        $mangled = /_Z[a-zA-Z0-9_]+B/  // Mangled symbol with 'B' tag
        $pe_magic = {4D 5A}            // MZ header
    condition:
        $pe_magic at 0 and #mangled > 0
}

Sigma Rule

title: Binutils Crash via Crafted PE File
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects crashes of Binutils tools due to CVE-2025-66866
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith:
            - '/objdump'
            - '/nm'
            - '/c++filt'
        ExitCode: -11  # SIGSEGV
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-66866 Binutils DoS via PE"; flow:to_client; content:"|4D 5A|"; offset:0; depth:2; content:"_Z"; distance:0; within:100; pcre:"/_Z[a-zA-Z0-9_]+B/"; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Avoid processing untrusted PE files with Binutils 2.26. Use alternative tools like readpe or pev.
2. Short-term: Apply vendor patch when available. Monitor Binutils releases for updates.
3. Long-term: Implement file validation before processing with Binutils. Use sandboxed environments for analysis.
4. Detection: Deploy YARA/Sigma rules to identify malicious PE files and monitor for crashes.

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