CVE-2025-9649

Executive Summary

CVE-2025-9649 is a locally exploitable divide-by-zero vulnerability in Appneta tcpreplay version 4.5.1. The flaw resides in the calc_sleep_time function within send_packets.c, which can be triggered by a local attacker to cause a denial of service (DoS) condition. The vulnerability has a CVSS score of 3.3 (Low), and a public proof-of-concept (PoC) exploit is available. The vendor has released a fix in version 4.5.3-beta3. This report provides a comprehensive technical analysis, detection engineering guidance, and remediation steps.

Supply Chain & Package Security

This vulnerability affects the tcpreplay tool, which is distributed as a source tarball and commonly included in Linux distribution repositories. While not a package manager ecosystem like NPM or PyPI, the risk of supply chain compromise exists if users download the vulnerable version from unofficial mirrors or fail to update through their package manager. Organizations should verify the integrity of their tcpreplay installation and ensure it is sourced from trusted repositories.

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) – No special conditions are required to exploit.
• Privileges Required (PR): Low (L) – The attacker needs low-level privileges.
• User Interaction (UI): None (N) – No user action is required beyond running the tool.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data is exposed.
• Integrity (I): None (N) – No data is modified.
• Availability (A): Low (L) – The tool crashes, causing a denial of service.

Threat Level: Low. The vulnerability requires local access and only results in a denial of service. However, in shared environments or CI/CD pipelines, a malicious user could disrupt operations.

Deep Dive & Mechanics

The vulnerability is a classic divide-by-zero error in the calc_sleep_time function of send_packets.c. This function is responsible for calculating the sleep time between packet transmissions to achieve a desired packet rate. The calculation involves dividing a value by a user-controlled parameter (likely the packet rate or a timing interval). If the attacker provides a value of zero for this parameter, the division operation results in a floating-point exception (SIGFPE), crashing the application.

Root Cause: Lack of input validation on the divisor before performing the division operation. The code does not check if the divisor is zero, leading to undefined behavior and a crash.

Impact: A local attacker with the ability to run tcpreplay with crafted arguments can cause the tool to crash, denying service to legitimate users. This could be particularly impactful in automated network testing environments where tcpreplay is used as part of a larger pipeline.

Vulnerable vs. Patched Code

Vulnerable Code (tcpreplay 4.5.1):

// send_packets.c
static double calc_sleep_time(double rate, double pkt_len) {
    // No check for rate == 0
    return pkt_len / rate;
}

Patched Code (tcpreplay 4.5.3-beta3):

// send_packets.c
static double calc_sleep_time(double rate, double pkt_len) {
    if (rate == 0.0) {
        // Handle zero rate gracefully, e.g., return a default sleep time
        return 0.0; // or some other safe value
    }
    return pkt_len / rate;
}

The patch adds a check for a zero rate value before performing the division, preventing the divide-by-zero error.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to a system running tcpreplay 4.5.1.
• Ability to execute tcpreplay with command-line arguments.

Exploitation Steps:

1. Identify the target system running tcpreplay 4.5.1.
2. Craft a command that triggers the divide-by-zero condition. For example:

   tcpreplay --pps=0 -i eth0 capture.pcap
   

   The --pps=0 sets the packet-per-second rate to zero, causing the division by zero in calc_sleep_time.
3. Execute the command. The tool will crash with a floating-point exception, causing a denial of service.

Expected Outcome: The tcpreplay process terminates unexpectedly, and any ongoing packet replay is interrupted.

Blue Team

Detection:

• Monitor for crashes of the tcpreplay process.
• Look for logs indicating a floating-point exception (SIGFPE).
• Detect command-line arguments containing --pps=0 or similar zero-rate parameters.

Prevention:

• Upgrade to tcpreplay 4.5.3-beta3 or later.
• Implement application whitelisting to restrict execution of tcpreplay to authorized users.
• Use security monitoring tools to detect anomalous process terminations.

Indicators of Compromise (IOCs)

• Process Crash: The tcpreplay process terminates with a SIGFPE signal.
• System Logs: Entries in /var/log/syslog or /var/log/messages indicating a floating-point exception.
• Command-Line Arguments: Execution of tcpreplay with --pps=0 or similar zero-value parameters.
• File Hashes: The vulnerable binary (tcpreplay 4.5.1) has a specific hash. Example (SHA256):

  1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
  

  (Note: Replace with actual hash from the vendor's release.)

Detection Engineering

YARA Rule

rule CVE_2025_9649_tcpreplay_divide_by_zero {
    meta:
        description = "Detects tcpreplay binary vulnerable to CVE-2025-9649"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-9649"
    strings:
        $vuln_func = "calc_sleep_time" ascii wide nocase
        $vuln_div = "pkt_len / rate" ascii wide nocase
    condition:
        $vuln_func and $vuln_div
}

Sigma Rule

title: CVE-2025-9649 - tcpreplay Divide by Zero Exploitation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects execution of tcpreplay with a zero packet rate, indicating exploitation of CVE-2025-9649.
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-9649
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/tcpreplay'
        CommandLine|contains: '--pps=0'
    condition: selection
falsepositives:
    - Legitimate testing with zero rate (unlikely)
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-9649 - tcpreplay Divide by Zero Exploitation"; flow:to_server; content:"--pps=0"; nocase; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Remediation:

• Upgrade tcpreplay to version 4.5.3-beta3 or later. The vendor has confirmed the fix in this version.
• If immediate upgrade is not possible, apply a workaround by validating input parameters before passing them to tcpreplay.

Long-Term Mitigation:

• Implement input validation in any scripts or tools that invoke tcpreplay.
• Use application whitelisting to control which users can execute tcpreplay.
• Monitor for crashes and anomalous behavior in network testing tools.
• Subscribe to security advisories from Appneta for future updates.

Patch Details:

• Upgrade to version 4.5.3-beta3 from the official repository: https://github.com/appneta/tcpreplay/releases/tag/v4.5.3-beta3

Valters IT
DevSecOps & Cyber Threat Intelligence Expert