CVE-2025-69647

Executive Summary

CVE-2025-69647 is a denial-of-service (DoS) vulnerability in the readelf utility of GNU Binutils through version 2.45.1. The flaw resides in the DWARF debugging information parser, specifically when processing malformed location lists (loclists) data. A logic error causes readelf to enter an infinite loop, repeatedly printing the same table output without making forward progress. This leads to unbounded CPU and I/O consumption, effectively hanging the tool until externally terminated. A local attacker can exploit this by supplying a crafted binary file, making it a low-complexity, low-privilege attack vector. No patch is currently available, and no public proof-of-concept (PoC) or exploit code has been released.

Supply Chain & Package Security

This vulnerability affects the GNU Binutils package, which is a core component in most Linux distributions and is often used in development and debugging toolchains. While not a direct supply chain injection, the tool is frequently used in CI/CD pipelines, automated analysis, and security scanning. An attacker who can inject a malicious binary into such a pipeline could cause a denial-of-service condition, disrupting builds or analysis workflows. The package is distributed via official repositories (e.g., apt, yum) and source tarballs from the GNU project.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (NVD) | Adjusted Score: 5.5 (Medium)

Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Threat Level: Medium. The attack requires local access and user interaction, but the impact is a complete hang of a common debugging tool, which can disrupt development and analysis workflows.

Deep Dive & Mechanics

The vulnerability is in the DWARF debugging information parser within readelf.c. The DWARF standard defines location lists (.debug_loclists) that describe variable locations across address ranges. The parser iterates over these lists, printing entries. A logic flaw in the loop control causes the parser to fail to advance the internal pointer when encountering malformed data, such as an invalid length field or a corrupted offset. Instead of skipping the entry or terminating, the code re-reads the same data, leading to an infinite loop.

Root Cause: In the function display_debug_loc (or similar), the loop that processes location list entries does not properly handle cases where the length of an entry is zero or negative, or where the entry type is unexpected. The loop condition checks for a sentinel value but does not increment the pointer when the entry is malformed, causing it to repeatedly process the same entry.

Trigger: A crafted ELF binary with a malformed .debug_loclists section. The attacker can manipulate the length fields or entry types to cause the parser to stall.

Impact: The readelf process consumes 100% CPU and generates unbounded output to stdout/stderr, filling disk space and potentially causing a system-wide DoS if run in a constrained environment.

Vulnerable vs. Patched Code

Vulnerable Code (GNU Binutils 2.45.1):

// Simplified representation of the vulnerable loop
while (1) {
    // Read entry type
    unsigned char entry_type = read_byte(data);
    if (entry_type == DW_LLE_end_of_list) break;

    // Read length (vulnerable: no validation)
    unsigned long length = read_uleb128(data);
    // Process entry based on type
    switch (entry_type) {
        case DW_LLE_offset_pair:
            // ... print and advance
            break;
        case DW_LLE_base_address:
            // ... print and advance
            break;
        default:
            // Missing: advance pointer by length
            // Falls through without advancing
            break;
    }
    // Loop continues without advancing data pointer
}

Patched Code (Hypothetical Fix):

while (1) {
    unsigned char entry_type = read_byte(data);
    if (entry_type == DW_LLE_end_of_list) break;

    unsigned long length = read_uleb128(data);
    // Validate length
    if (length == 0 || length > remaining_data) {
        // Skip malformed entry
        break; // or advance to next section
    }
    switch (entry_type) {
        case DW_LLE_offset_pair:
            // ... print and advance
            break;
        case DW_LLE_base_address:
            // ... print and advance
            break;
        default:
            // Advance pointer by length
            data += length;
            break;
    }
}

The fix ensures that for any unknown or malformed entry, the parser either skips the entry by advancing the pointer or terminates the loop.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to a system with GNU Binutils 2.45.1 or earlier.
• Ability to create a binary file.

Steps:

1. Create a minimal ELF binary with a malformed .debug_loclists section.
2. Use a hex editor or a script to craft the section:
   • Set the section type to SHT_PROGBITS with name .debug_loclists.
   • Insert a location list header with a corrupted length field (e.g., length = 0).
   • Include an entry type that is not handled (e.g., DW_LLE_GNU_view_pair).
3. Run readelf --debug-dump=loc my_malicious_binary.
4. Observe that readelf hangs indefinitely, consuming CPU and generating output.

Example Crafting Script (Python):

import struct

# Minimal ELF header (64-bit)
elf = bytearray(b'\x7fELF\x02\x01\x01\x00' + b'\x00'*8)
# ... (full ELF construction omitted for brevity)

# Malformed .debug_loclists section
loclists = bytearray()
# Header: version, address size, segment size
loclists += struct.pack('<H', 5)  # version
loclists += struct.pack('B', 8)   # address size
loclists += struct.pack('B', 0)   # segment size
# Entry: type 0x05 (DW_LLE_base_addressx) with length 0
loclists += b'\x05'  # entry type
loclists += b'\x00'  # length (ULEB128 = 0)
# No end-of-list marker

# Write to file
with open('malicious.elf', 'wb') as f:
    f.write(elf + loclists)

Blue Team (Defense)

Detection:

• Monitor for readelf processes running for an abnormally long time.
• Use resource monitoring to detect high CPU usage by readelf.
• Implement file scanning to detect malformed ELF binaries with suspicious DWARF sections.

Mitigation:

• Restrict execution of readelf on untrusted files.
• Use a sandbox or container for binary analysis.
• Apply resource limits (e.g., ulimit -t 10 to limit CPU time).

Indicators of Compromise (IOCs)

• File Hashes: (Example, not real) sha256: a1b2c3d4e5f6...
• Process Name: readelf
• Behavior: Infinite loop, 100% CPU usage, unbounded stdout/stderr output.
• Network: None (local-only attack).
• Registry/File System: Presence of a crafted ELF binary with a malformed .debug_loclists section.

Detection Engineering

YARA Rule

rule CVE_2025_69647_Readelf_DoS {
    meta:
        description = "Detects malformed ELF binaries exploiting CVE-2025-69647"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-69647"
    strings:
        $elf_magic = { 7f 45 4c 46 }
        $loclists_name = ".debug_loclists"
        $malformed_entry = { 05 00 }  // entry type 0x05 with length 0
    condition:
        $elf_magic at 0 and $loclists_name and $malformed_entry
}

Sigma Rule

title: CVE-2025-69647 - Readelf Infinite Loop DoS
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects readelf process consuming excessive CPU due to malformed DWARF data
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image: /usr/bin/readelf
        CommandLine: '*--debug-dump=loc*'
    condition: selection
    timeframe: 30s
    aggregation:
        - field: Image
          function: count
          condition: gt 5
falsepositives:
    - Legitimate analysis of large binaries
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-69647 - Malformed ELF with DWARF loclists"; flow:to_client; content:"|7f 45 4c 46|"; offset:0; depth:4; content:".debug_loclists"; within:100; content:"|05 00|"; within:10; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Avoid using readelf on untrusted binaries. Use alternative tools like objdump or llvm-dwarfdump which may not be vulnerable.
2. Apply resource limits: Use ulimit -t 10 to limit CPU time for readelf processes.
3. Monitor for exploitation: Deploy the YARA/Sigma rules to detect malicious binaries.

Long-Term Fix:

• Wait for an official patch from GNU Binutils. The fix should validate DWARF loclists entry lengths and ensure the parser always advances the pointer.
• Consider applying a vendor-specific patch if available (e.g., from Red Hat or Debian).

Workaround:

• Patch the source code locally by adding a check for zero-length entries and advancing the pointer in the default case of the switch statement.

Valters IT