CVE-2022-32208: Haxx Curl FTP Krb5 MITM Vulnerability

CVE-2022-32208 Overview

CVE-2022-32208 is a Man-in-the-Middle vulnerability affecting curl versions prior to 7.84.0 when performing FTP transfers secured by Kerberos 5 (krb5) authentication. The vulnerability stems from improper handling of message verification failures during the krb5 security handshake, which allows attackers positioned on the network path to intercept and potentially inject malicious data into FTP communications without detection.

When curl establishes a krb5-secured FTP connection, it relies on cryptographic message verification to ensure data integrity and authenticity. However, due to flawed error handling in affected versions, verification failures are not properly acted upon, creating a window of opportunity for network-based attackers to manipulate traffic.

Critical Impact

Attackers can silently intercept krb5-secured FTP transfers, potentially exfiltrating sensitive data or injecting malicious content without triggering any security warnings to the client.

Affected Products

• Haxx curl versions prior to 7.84.0
• Fedora 35
• Debian Linux 10.0 and 11.0
• NetApp Clustered Data ONTAP, Element Software, HCI Management Node, SolidFire
• NetApp HCI Compute Node, Bootstrap OS
• NetApp H300S, H500S, H700S, H410S (and associated firmware)
• Apple macOS (various versions)
• Splunk Universal Forwarder

Discovery Timeline

• 2022-07-07 - CVE-2022-32208 published to NVD
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2022-32208

Vulnerability Analysis

This vulnerability affects curl's implementation of FTP transfers using Kerberos 5 authentication. The flaw exists in how curl processes cryptographic message verification during the security layer negotiation phase of krb5-authenticated FTP sessions.

During normal krb5-secured FTP operations, the client and server exchange authenticated messages that are verified using cryptographic mechanisms to ensure they haven't been tampered with. The vulnerability occurs because curl fails to properly terminate the connection or alert the user when these verification checks fail. Instead of rejecting unverified or tampered messages, curl continues processing them, effectively rendering the security layer useless.

This behavior allows a Man-in-the-Middle attacker who has positioned themselves between the curl client and the FTP server to:

1. Intercept encrypted traffic without triggering verification errors
2. Modify data in transit without detection
3. Inject arbitrary data into the FTP stream

The attack requires network positioning (such as ARP spoofing, DNS hijacking, or control of intermediate network infrastructure) but does not require authentication or user interaction once the attacker is positioned.

Root Cause

The root cause lies in improper error handling within curl's krb5 FTP authentication module. When the Kerberos library returns a verification failure for incoming messages, curl's code path fails to treat this as a fatal error condition. The CWE classifications (CWE-840: Business Logic Errors, CWE-787: Out-of-bounds Write) indicate that the vulnerability involves both logical flow issues in security handling and potential memory safety concerns.

Specifically, the verification result is either ignored or insufficiently checked before proceeding with data processing, violating the fundamental security guarantee that krb5 authentication is supposed to provide.

Attack Vector

The attack vector is network-based and requires the attacker to be positioned in the network path between the curl client and the target FTP server. The attack scenario unfolds as follows:

1. The victim initiates a krb5-secured FTP connection using a vulnerable curl version
2. The attacker intercepts the connection using network-level positioning techniques
3. During the krb5 handshake or subsequent data transfer, the attacker modifies or replaces messages
4. Curl's faulty verification handling fails to detect the tampering
5. The attacker can now read sensitive data or inject malicious content into the FTP transfer

This vulnerability is particularly concerning in enterprise environments where FTP with Kerberos authentication is used for secure file transfers, as the security mechanism designed to prevent such attacks becomes ineffective.

Detection Methods for CVE-2022-32208

Indicators of Compromise

• Unexpected FTP data content or file modifications after transfers using krb5 authentication
• Network traffic anomalies between curl clients and FTP servers, particularly during authentication phases
• Evidence of ARP spoofing, DNS poisoning, or other network positioning attacks in conjunction with krb5-FTP traffic
• Log entries showing unusual FTP session behavior or connection resets during krb5 negotiations

Detection Strategies

• Inventory all systems running curl and identify versions below 7.84.0 that may utilize krb5-secured FTP
• Monitor network traffic for signs of Man-in-the-Middle attacks targeting FTP connections on standard ports (20, 21) and passive mode ranges
• Implement network intrusion detection rules to flag anomalous Kerberos ticket exchanges or replay attempts
• Review FTP server logs for unusual client behavior or authentication patterns

Monitoring Recommendations

• Deploy endpoint detection and response (EDR) solutions like SentinelOne to monitor curl process behavior and network connections
• Enable verbose logging for FTP transfers in enterprise environments to capture authentication handshake details
• Implement network segmentation to limit exposure of krb5-FTP traffic to potential attackers
• Configure SIEM rules to correlate FTP authentication events with network anomaly detection alerts

How to Mitigate CVE-2022-32208

Immediate Actions Required

• Upgrade curl to version 7.84.0 or later on all affected systems immediately
• Audit systems for curl installations, including embedded versions in applications like Splunk Universal Forwarder
• Apply vendor-specific patches from Apple, NetApp, Debian, and Fedora as appropriate for your environment
• Consider temporarily disabling krb5-authenticated FTP transfers until patches are applied

Patch Information

The vulnerability is fixed in curl version 7.84.0 and later. Multiple vendors have released security updates addressing this issue:

• Haxx: Curl 7.84.0 contains the fix for this vulnerability
• Debian: Security advisories DSA-5197 and updates via debian-lts-announce
• Fedora: Package updates available via the Fedora Package Announcement
• Apple: macOS updates documented in HT213488
• NetApp: Advisory NTAP-20220915-0003
• Gentoo: Security advisory GLSA-202212-01

Additional technical details about the vulnerability are available in the HackerOne Report #1590071.

Workarounds

• Avoid using FTP with krb5 authentication on untrusted networks until the patch is applied
• Use alternative secure file transfer protocols such as SFTP or SCP that are not affected by this vulnerability
• Implement VPN or other encrypted tunnels to protect FTP traffic from network-level interception
• Deploy network access controls to limit which systems can communicate with FTP servers using Kerberos authentication

# Check curl version on your system
curl --version

# Example: Update curl on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade curl

# Example: Update curl on RHEL/CentOS/Fedora systems
sudo dnf update curl