CVE-2026-44074

Executive Summary

CVE-2026-44074 is a low-severity vulnerability in Netatalk, an open-source implementation of the Apple Filing Protocol (AFP). The flaw resides in the error-handling logic, where multiple errno values are combined using a bitwise OR operation. When multiple error conditions occur simultaneously, this results in incorrect error codes, potentially leading to a minor service disruption. The vulnerability affects Netatalk versions 2.1.0 through 4.4.2. No public proof-of-concept (PoC) or exploit code is currently available, and the vendor has not released a patch. The EPSS score is 0.0%, indicating a very low probability of exploitation in the wild.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Base Score: 3.7 (Low)
• Attack Vector: Network (AV:N)
• 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: Low (A:L)

The threat level is low due to the minimal impact on availability and the absence of any impact on confidentiality or integrity. The vulnerability is remotely exploitable without authentication, but the complexity is low, and no user interaction is required.

Deep Dive & Mechanics

The core issue is a logic error in the error-handling code of Netatalk. When multiple error conditions occur simultaneously (e.g., during a network connection or file operation), the code combines the errno values using a bitwise OR operation. This is incorrect because errno values are not bitwise-compatible; they are distinct integer values representing different error types. The bitwise OR produces a composite value that does not correspond to any single error, leading to incorrect error-handling paths.

For example, if errno is set to EACCES (13) and EIO (5) simultaneously, the bitwise OR would yield 13 | 5 = 13 (since 13 in binary is 1101 and 5 is 0101, OR gives 1101 = 13). This might incorrectly map to EACCES and skip handling for EIO. Conversely, if errno is EAGAIN (11) and EINTR (4), the OR yields 11 | 4 = 15, which is not a standard errno value, potentially causing undefined behavior or a crash.

The vulnerability is triggered by network conditions that cause multiple errors to occur in rapid succession, such as a malformed AFP request that triggers both a permission error and an I/O error. The incorrect error code then leads to a failure in the expected error recovery, resulting in a denial-of-service condition (e.g., the AFP service becoming unresponsive or crashing).

Vulnerable vs. Patched Code

The vulnerable code pattern is found in the error-handling routines of Netatalk, likely in the afpd daemon or related libraries. The flawed logic uses a bitwise OR to combine errno values:

// Vulnerable code (pseudocode)
int combined_errno = errno1 | errno2;
if (combined_errno == EACCES) {
    // handle permission error
} else if (combined_errno == EIO) {
    // handle I/O error
}

A patched version would use logical OR or separate checks:

// Patched code (pseudocode)
if (errno1 == EACCES || errno2 == EACCES) {
    // handle permission error
}
if (errno1 == EIO || errno2 == EIO) {
    // handle I/O error
}

Since no official patch is available, the fix must be applied manually by the maintainer or by users applying a workaround.

Exploitation & Lab Setup

Red Team

No public exploit code is available. To simulate the vulnerability in a lab environment, an attacker would need to craft network packets that trigger multiple error conditions simultaneously. This could be done by sending malformed AFP requests that cause both a permission error (e.g., accessing a restricted directory) and an I/O error (e.g., a disk read failure). The following Python script using scapy can be used to send a crafted AFP request:

#!/usr/bin/env python3
from scapy.all import *
import socket

target_ip = "192.168.1.100"
target_port = 548  # AFP default port

# Craft a malformed AFP request (simplified)
# This is a placeholder; actual AFP packet structure is complex
payload = b"\x00\x03\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(payload)
response = sock.recv(1024)
sock.close()
print(f"Response: {response}")

This script sends a malformed packet that may trigger multiple errors. The attacker would then monitor the AFP service for crashes or unresponsiveness.

Blue Team

To detect exploitation attempts, monitor AFP traffic for malformed packets or unusual error patterns. Use network intrusion detection systems (NIDS) to alert on anomalous AFP requests. Additionally, monitor system logs for AFP-related errors or crashes.

Indicators of Compromise (IOCs)

• Network: Malformed AFP packets with unusual combinations of error codes.
• System: AFP service (afpd) crashes or becomes unresponsive.
• Logs: Repeated error messages in /var/log/messages or AFP logs indicating unexpected error codes.
• File: Core dumps from afpd with unusual errno values.

Detection Engineering

YARA Rule

rule CVE_2026_44074_Netatalk_Error_Handling {
    meta:
        description = "Detects Netatalk binaries with vulnerable error-handling logic (bitwise OR on errno)"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-44074"
    strings:
        $errno_or = { 0B ?? 0B ?? 21 ?? }  // Pattern for bitwise OR on errno values (simplified)
    condition:
        $errno_or
}

Sigma Rule

title: CVE-2026-44074 - Netatalk Error Handling Vulnerability
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2026-44074 via malformed AFP packets
author: Valters IT
date: 2025-04-10
logsource:
    category: network
    product: suricata
detection:
    selection:
        app_proto: afp
        payload|contains: "00 03 00 00 00 01"  # Example malformed AFP header
    condition: selection
falsepositives:
    - Legitimate AFP traffic with similar patterns (rare)
level: low

Suricata Rule

alert tcp any any -> any 548 (msg:"CVE-2026-44074 - Netatalk Malformed AFP Request"; flow:to_server; content:"|00 03 00 00 00 01|"; depth:6; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate: Restrict network access to the AFP service (port 548) to trusted hosts only using firewall rules.
• Short-term: Monitor for updates from the Netatalk project. If no patch is available, consider disabling the AFP service if not required.
• Long-term: Apply the code fix described in the "Vulnerable vs. Patched Code" section once the vendor releases an update. Alternatively, switch to a different file-sharing protocol (e.g., SMB) if AFP is not essential.

Valters IT
DevSecOps & Cyber Threat Intelligence