CVE-2023-35704: Critical Buffer Overflow Vulnerabilities in GTKWave’s FST LEB128 Varint Functionality

Overview

The cybersecurity landscape is constantly evolving, with new vulnerabilities being discovered on a regular basis. One such vulnerability is the CVE-2023-35704, a serious security flaw identified in the GTKWave 3.3.115. This vulnerability is particularly concerning as it affects the FST LEB128 varint functionality of GTKWave, a widely used waveform viewer for Verilog RTL simulation.
The flaw is significant due to its potential to enable an attacker to execute arbitrary code, leading to full system compromise or potential data leakage. This could have severe implications for users, particularly those in industries where data security is paramount. As such, understanding this vulnerability and how to mitigate its risks is of the utmost importance.

Vulnerability Summary

CVE ID: CVE-2023-35704
Severity: High (7.8 CVSS Score)
Attack Vector: File-based (via a specially crafted .fst file)
Privileges Required: None
User Interaction: Required (victim needs to open the malicious file)
Impact: Arbitrary code execution leading to system compromise or data leakage

Affected Products

Product | Affected Versions

GTKWave | 3.3.115

How the Exploit Works

The exploit takes advantage of multiple stack-based buffer overflow vulnerabilities in the FST LEB128 varint functionality of GTKWave 3.3.115. An attacker crafts a malicious .fst file which, when opened by the victim, overflows the buffer, allowing the attacker to execute arbitrary code on the victim’s system. This is achieved through the manipulation of the fstReaderVarint32WithSkip function, which fails to properly handle specially crafted .fst files.

Conceptual Example Code

Here’s a conceptual example of how the vulnerability might be exploited. This is a simplified representation and actual exploit code may be more complex.

#include <stdio.h>
#include <string.h>
void malicious_fst_file() {
char buffer[10];
// a crafted .fst file with contents exceeding the buffer size
char *malicious_fst = "Exceedingly_long_and_malicious_file_content...";
strcpy(buffer, malicious_fst);
}
int main() {
malicious_fst_file();
return 0;
}

In this example, the `malicious_fst` string represents the malicious .fst file. When the `malicious_fst_file` function is executed, the buffer overflows due to the excessive length of the malicious .fst file, potentially leading to arbitrary code execution.

Mitigation Guidance

As a preventive measure, users are advised to apply the vendor patch as soon as it is available. This patch will fix the vulnerabilities present in the FST LEB128 varint functionality of GTKWave 3.3.115. In the interim, using a Web Application Firewall (WAF) or an Intrusion Detection System (IDS) can serve as temporary mitigation, providing some level of protection against potential attacks exploiting this vulnerability.