CVE-2020-24240 : What You Need to Know

GNU Bison before 3.7.1 has a use-after-free vulnerability in _obstack_free in lib/obstack.c when encountering a '\0' byte. This vulnerability poses a risk when Bison is used with untrusted input.

Understanding CVE-2020-24240

This CVE involves a use-after-free vulnerability in GNU Bison before version 3.7.1.

What is CVE-2020-24240?

CVE-2020-24240 is a use-after-free vulnerability in GNU Bison, specifically in the _obstack_free function in lib/obstack.c, triggered by encountering a '\0' byte. The risk is present when Bison processes untrusted input, potentially leading to unsafe behavior.

The Impact of CVE-2020-24240

The vulnerability may result in a crash within Bison itself, especially when used with specific compiler/architecture combinations. It does not necessarily lead to crashes in the generated code.

Technical Details of CVE-2020-24240

This section delves into the technical aspects of the vulnerability.

Vulnerability Description

The use-after-free vulnerability occurs in _obstack_free in lib/obstack.c, called from gram_lex, when a '\0' byte is encountered during processing.

Affected Systems and Versions

Product: Not applicable
Vendor: Not applicable
Versions affected: All versions before 3.7.1

Exploitation Mechanism

Exploitation requires the presence of a '\0' byte in the input
Risk is heightened when Bison processes untrusted input

Mitigation and Prevention

Protecting systems from CVE-2020-24240 involves immediate steps and long-term security practices.

Immediate Steps to Take

Update Bison to version 3.7.1 or later
Avoid using Bison with untrusted input

Long-Term Security Practices

Regularly update software and libraries
Implement input validation and sanitization mechanisms

Patching and Updates

Apply patches provided by GNU Bison to address the use-after-free vulnerability