CVE-2025-11839

Executive Summary

CVE-2025-11839 is a locally exploitable security flaw in GNU Binutils version 2.45. The vulnerability resides in the tg_tag_type function within the prdbg.c file, where the return value of a manipulation is not checked. This unchecked return value can lead to undefined behavior, potentially causing a denial of service or other unspecified impacts. The attack vector is local, requiring an attacker to have some level of access to the system. The exploit has been publicly released, increasing the risk of active exploitation. The CVSS score is 3.3 (Low), reflecting the local attack vector and limited impact.

CVSS Breakdown & Threat Level

• CVSS Score: 3.3 (Low)
• Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
• Attack Vector (AV): Local (L) - The attacker must have local access to the system.
• Attack Complexity (AC): Low (L) - The attack does not require special conditions.
• Privileges Required (PR): Low (L) - The attacker needs low-level privileges.
• User Interaction (UI): None (N) - No user interaction is required.
• Scope (S): Unchanged (U) - The impact is confined to the vulnerable component.
• Confidentiality (C): None (N) - No data confidentiality impact.
• Integrity (I): None (N) - No data integrity impact.
• Availability (A): Low (L) - The vulnerability can cause a denial of service or performance degradation.

Threat Level: Low. The local attack vector and low impact reduce the immediate threat, but the public exploit availability warrants attention for systems where untrusted users have local access.

Deep Dive & Mechanics

The vulnerability is located in the tg_tag_type function within prdbg.c of GNU Binutils 2.45. This function is part of the debug information processing subsystem. The flaw involves an unchecked return value from a manipulation performed within the function. In C, failing to check return values can lead to the use of invalid pointers, buffer overflows, or other undefined behavior if the operation fails.

The specific manipulation is not detailed in the public description, but it likely involves a memory allocation or a string operation that can fail. If the return value is not checked, the function may proceed with a corrupted state, potentially leading to a crash or exploitable condition. Since the attack is local, an attacker could craft a malicious binary or debug information file that triggers this code path when processed by objdump, readelf, or other Binutils tools.

Vulnerable vs. Patched Code

Vulnerable Code (GNU Binutils 2.45 - prdbg.c):

// Hypothetical vulnerable snippet
static void
tg_tag_type (void *p, int tag, const char *name)
{
    struct pr_dbg_info *info = (struct pr_dbg_info *) p;
    char *new_name = strdup (name); // Return value not checked
    // ... use new_name without checking if strdup failed
}

Patched Code (Hypothetical):

static void
tg_tag_type (void *p, int tag, const char *name)
{
    struct pr_dbg_info *info = (struct pr_dbg_info *) p;
    char *new_name = strdup (name);
    if (new_name == NULL) {
        // Handle allocation failure
        return;
    }
    // ... use new_name safely
}

The patch would involve adding a check for the return value of the operation (e.g., strdup, malloc, or similar) and handling the failure case appropriately, such as by returning early or cleaning up.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a system with GNU Binutils 2.45 installed.
• Ability to create a malicious binary or debug info file.

Exploitation Steps:

1. Craft a malicious ELF binary or debug information file that triggers the tg_tag_type function with a crafted input that causes the unchecked operation to fail.
2. Use a tool like objdump or readelf to process the malicious file:

   objdump -g malicious_binary
   

3. The unchecked return value may cause a crash or undefined behavior, potentially allowing for denial of service or further exploitation.

Note: No public exploit code is available in the provided data, but the vulnerability is confirmed as exploitable.

Blue Team

Detection:

• Monitor for crashes or abnormal behavior in Binutils tools (objdump, readelf, size, etc.).
• Use file integrity monitoring to detect the introduction of suspicious binary files.
• Implement application whitelisting to restrict which users can run Binutils tools.

Mitigation:

• Restrict local access to trusted users only.
• Monitor logs for repeated crashes of Binutils tools.
• Consider using a sandbox or container for processing untrusted binaries.

Indicators of Compromise (IOCs)

• File Hashes: (None provided; would be generated from known malicious samples)
• Process Names: objdump, readelf, size, nm, strings (when processing malicious files)
• Log Entries: Core dumps or segmentation faults in Binutils tools.
• Network: None (local vulnerability).

Detection Engineering

YARA Rule

rule CVE_2025_11839_Binutils_Unchecked_Return {
    meta:
        description = "Detects potential exploitation of CVE-2025-11839 in GNU Binutils"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-11839"
    strings:
        $s1 = "tg_tag_type" ascii wide nocase
        $s2 = "prdbg.c" ascii wide nocase
    condition:
        $s1 and $s2
}

Sigma Rule

title: CVE-2025-11839 Binutils Unchecked Return Value
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects crashes or abnormal behavior in GNU Binutils tools potentially related to CVE-2025-11839
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith:
            - '/objdump'
            - '/readelf'
            - '/size'
            - '/nm'
            - '/strings'
        ExitCode: 139  # SIGSEGV
    condition: selection
falsepositives:
    - Legitimate crashes due to corrupted files
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-11839 Binutils Local Exploit Attempt"; flow:to_server; content:"|00|"; depth:1; classtype:attempted-dos; sid:1000001; rev:1;)

Note: Suricata rule is generic as the vulnerability is local; network detection is not directly applicable.

Remediation & Mitigation

Immediate Actions:

1. Restrict Access: Limit local user access to systems running GNU Binutils 2.45.
2. Monitor: Enable logging and monitoring for crashes of Binutils tools.
3. Sandbox: Process untrusted binaries in isolated environments (containers, VMs).

Long-term Fix:

• Apply a patch from the vendor when available. Since the patch status is UNKNOWN, consider:
  • Upgrading to a newer version of GNU Binutils if available.
  • Applying a manual patch to prdbg.c to check return values.
  • Using a third-party security patch or workaround.

Workaround:

• Avoid using Binutils tools to process untrusted files from unprivileged users.

Valters IT
Securing Digital Frontiers