CVE-2023-35956: Heap-Based Buffer Overflow Vulnerability in GTKWave

Overview

Security vulnerabilities are a significant concern for software developers and users alike. In this post, we’ll discuss a particular vulnerability identified as CVE-2023-35956 that impacts the GTKWave software, version 3.3.115. This vulnerability is of serious concern due to its potential to enable arbitrary code execution, leading to potential system compromise or data leakage.
GTKWave is a fully featured GTK+ based wave viewer used for viewing VCD files (Value Change Dump). It is widely employed in systems where waveform viewing is necessary, especially in digital design environments. Therefore, this vulnerability could potentially affect a wide range of users, and addressing it is of utmost importance.

Vulnerability Summary

CVE ID: CVE-2023-35956
Severity: High (7.8 CVSS Score)
Attack Vector: Local
Privileges Required: User
User Interaction: Required
Impact: Potential system compromise or data leakage

Affected Products

Product | Affected Versions

GTKWave | 3.3.115

How the Exploit Works

The vulnerability in question stems from multiple heap-based buffer overflow vulnerabilities in the fstReaderIterBlocks2 VCDATA parsing functionality of GTKWave. Buffer overflow vulnerabilities typically occur when data is written into a buffer and surpasses the buffer’s boundary, consequently overwriting adjacent memory locations.
In this case, a specially-crafted .fst file can lead to arbitrary code execution. A victim would need to open this maliciously crafted file, triggering the vulnerability. The decompression function `fastlz_decompress` is the primary concern in this vulnerability.

Conceptual Example Code

Here is a conceptual representation of how an exploit of this vulnerability might look. This pseudocode demonstrates the overflow occurring when a maliciously oversized .fst file is loaded:

# Pseudocode
def load_fst_file(file):
with open(file, 'r') as f:
data = f.read()
return fastlz_decompress(data)
# Exploit
malicious_fst = generate_oversized_fst()  # A function that generates a malicious .fst file
load_fst_file(malicious_fst)

In this example, the `load_fst_file` function reads a file and then decompresses it using the `fastlz_decompress` function. If a maliciously oversized .fst file is loaded, it could cause a buffer overflow and potentially allow arbitrary code execution.
Please note that this is a highly simplified representation of the actual process and is meant only to provide a conceptual understanding of how such an exploit might work.

Mitigation Guidance

Users of affected versions of GTKWave are advised to apply the vendor-supplied patch as soon as possible. If for some reason the patch cannot be applied immediately, a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can provide temporary mitigation by monitoring the traffic and potentially blocking attempts to exploit this vulnerability.