CVE-2025-48056

Executive Summary

CVE-2025-48056 is a medium-severity vulnerability in the Hubble CLI component of Cilium, a cloud-native networking and security observability platform. The flaw allows a network attacker to inject malicious control characters into the terminal output of the Hubble CLI when monitoring Kafka traffic with Layer 7 Protocol Visibility enabled. This injection can lead to loss of integrity and manipulation of the displayed output, potentially allowing an attacker to conceal log entries, rewrite output, or temporarily render the terminal unusable. The vulnerability is patched in Hubble CLI v1.17.2. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the attack vector is network-based and requires user interaction (monitoring Kafka traffic).

Supply Chain & Package Security

Hubble CLI is distributed as part of the Cilium ecosystem, typically via container images or binary releases. Users should verify the integrity of their Hubble CLI binaries using checksums provided by the official Cilium releases. The vulnerability does not directly affect the Cilium agent or operator, but the CLI tool is commonly used by operators and security teams for real-time observability.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L
• Base Score: 5.3 (Medium)
• Attack Vector (AV): Network – the attacker can send malicious Kafka traffic over the network.
• Attack Complexity (AC): Low – no special conditions required.
• Privileges Required (PR): None – attacker does not need authentication.
• User Interaction (UI): Required – the victim must be actively monitoring Kafka traffic with Hubble CLI.
• Scope (S): Unchanged – the vulnerability affects the CLI output only.
• Confidentiality (C): None – no data is exposed.
• Integrity (I): Low – output can be manipulated.
• Availability (A): Low – terminal can be temporarily unusable.

Threat Level: Medium. Exploitation requires specific conditions (Kafka monitoring with L7 visibility), but the impact on integrity and availability is limited.

Deep Dive & Mechanics

The vulnerability resides in how Hubble CLI processes and displays Kafka protocol data when Layer 7 Protocol Visibility is enabled. Kafka messages can contain arbitrary binary data, including control characters (e.g., ANSI escape sequences, carriage returns, backspace characters). When Hubble CLI renders these messages to the terminal without proper sanitization, an attacker can inject sequences that:

• Conceal log entries: Use carriage returns (\r) or backspace (\b) to overwrite previously displayed lines.
• Rewrite output: Inject ANSI escape codes to change text color, position, or content.
• Make terminal unusable: Send sequences that lock the terminal (e.g., \x1b[?25l to hide cursor, or infinite scrolling).

The attack is triggered when a victim runs hubble observe --protocol kafka (or similar) and a malicious Kafka producer sends crafted messages. The attacker does not need to be on the same network segment; they only need to be able to send Kafka messages to a broker that the victim is monitoring.

Vulnerable vs. Patched Code

Vulnerable Code (pre-1.17.2): The Hubble CLI likely used a simple fmt.Fprintf or fmt.Println to output Kafka message payloads without escaping control characters.

// Vulnerable example (conceptual)
fmt.Printf("Message: %s\n", kafkaMessage.Payload)

Patched Code (1.17.2+): The fix involves sanitizing the output by escaping or stripping control characters before display. This can be done using functions like strings.ReplaceAll or a dedicated sanitizer.

// Patched example (conceptual)
sanitizedPayload := sanitizeControlChars(kafkaMessage.Payload)
fmt.Printf("Message: %s\n", sanitizedPayload)

func sanitizeControlChars(s string) string {
    // Replace control characters with visible representations
    s = strings.ReplaceAll(s, "\r", "\\r")
    s = strings.ReplaceAll(s, "\b", "\\b")
    s = strings.ReplaceAll(s, "\x1b", "\\e")
    // ... other control chars
    return s
}

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• A Kafka broker accessible from the attacker's machine.
• A victim running Hubble CLI with L7 Kafka visibility (e.g., hubble observe --protocol kafka).
• Ability to produce messages to a Kafka topic.

Exploitation Steps:

1. Identify a Kafka topic that the victim is monitoring.
2. Craft a malicious Kafka message containing control characters. For example, to overwrite the previous line:

   \r[+] Connection successful
   

   Or to hide a log entry:

   \x1b[2K\r[+] All clear
   

3. Send the message using a Kafka producer (e.g., kafka-console-producer).
4. The victim's terminal will display the manipulated output.

Example Payload (Python):

from kafka import KafkaProducer
producer = KafkaProducer(bootstrap_servers='victim-kafka:9092')
payload = b'\r[+] Connection successful\n\x1b[2K\r[+] All clear'
producer.send('monitored-topic', payload)
producer.flush()

Blue Team (Detection & Defense)

Detection:

• Monitor for unusual Kafka messages containing control characters (e.g., \x1b, \r, \b).
• Use network monitoring tools to inspect Kafka traffic for non-printable characters.
• Enable logging of Hubble CLI output to a file and inspect with a text editor (as recommended in the advisory).

Defense:

• Upgrade to Hubble CLI v1.17.2 or later.
• If upgrade is not possible, redirect Hubble flows to a log file and use a text editor that escapes control characters.
• Restrict Kafka producer access to trusted entities only.
• Implement input validation on Kafka messages to strip control characters at the broker level (if feasible).

Indicators of Compromise (IOCs)

• Network: Kafka messages containing ANSI escape sequences (\x1b[) or control characters (\r, \b, \n).
• Host: Hubble CLI output files containing unexpected control characters.
• Terminal: Unusual behavior such as text overwriting, cursor hiding, or terminal lockup when running hubble observe.

Detection Engineering

YARA Rule

rule CVE_2025_48056_Hubble_CLI_Control_Char_Injection {
    meta:
        description = "Detects malicious control characters in Kafka messages targeting Hubble CLI"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-48056"
    strings:
        $ansi_escape = /\x1b\[[0-9;]*[a-zA-Z]/
        $carriage_return = /\r/
        $backspace = /\b/
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-48056 - Hubble CLI Control Character Injection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects Kafka messages containing control characters that could exploit Hubble CLI
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-48056
logsource:
    category: network
    product: kafka
detection:
    selection:
        payload|contains:
            - '\x1b'
            - '\r'
            - '\b'
    condition: selection
falsepositives:
    - Legitimate use of control characters in Kafka messages (rare)
level: medium

Suricata Rule

alert tcp any any -> any 9092 (msg:"CVE-2025-48056 - Hubble CLI Control Character Injection in Kafka"; flow:to_server; content:"|1b|"; within:100; content:"|0d|"; within:100; classtype:attempted-user; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate:

• Upgrade Hubble CLI to version 1.17.2 or later.
• If upgrade is not possible, redirect Hubble flows to a log file and inspect with a text editor that escapes control characters.

Long-term:

• Implement input validation on Kafka messages to strip or escape control characters at the application level.
• Restrict Kafka producer access to trusted entities.
• Monitor for unusual terminal behavior in environments using Hubble CLI.

Patch Details:

• Upgrade to Hubble CLI v1.17.2 from the official Cilium repository.

Valters IT