CVE-2021-32256: GNU Binutils Buffer Overflow Vulnerability

CVE-2021-32256 Overview

A stack overflow vulnerability exists in GNU libiberty, as distributed in GNU Binutils 2.36. The vulnerability occurs in the demangle_type function within rust-demangle.c, which handles demangling of Rust symbol names. When processing specially crafted input, the function can be exploited to cause a stack overflow condition, leading to a denial of service.

Critical Impact

This stack overflow vulnerability allows remote attackers to cause denial of service through crafted input processed by the Rust demangling functionality in GNU Binutils.

Affected Products

• GNU Binutils 2.36

Discovery Timeline

• 2023-07-18 - CVE CVE-2021-32256 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-32256

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), specifically manifesting as a stack overflow within the Rust symbol demangling functionality. The demangle_type function in rust-demangle.c fails to properly handle certain edge cases in mangled Rust symbol names, leading to excessive recursion or unbounded stack allocation.

The vulnerability is exploitable via network-based attack vectors, though user interaction is required. An attacker could craft malicious input that, when processed by applications using GNU Binutils' demangling capabilities, triggers the stack overflow condition. This results in application crashes and denial of service scenarios.

Root Cause

The root cause lies in improper bounds checking within the demangle_type function when processing Rust mangled names. The function handles type demangling recursively, and crafted input can cause the recursion to exceed safe stack limits. This is a classic example of insufficient validation of input complexity before performing recursive operations, a common pattern in demangling and parsing code.

Attack Vector

The attack vector is network-based, requiring an attacker to deliver malformed Rust symbol data to a target application that utilizes GNU Binutils for symbol demangling. Common attack scenarios include:

• Processing malicious binary files or object files containing crafted symbol tables
• Parsing untrusted debug information or symbol dumps
• Applications that accept user-supplied input for symbol demangling operations

The exploitation does not require elevated privileges but does require user interaction, such as opening a malicious file or processing attacker-controlled data.

The vulnerability occurs when the demangle_type function processes deeply nested or recursive type structures in Rust mangled names. The function fails to implement adequate recursion depth limits, allowing stack exhaustion. For detailed technical analysis, see the Launchpad Bug Report.

Detection Methods for CVE-2021-32256

Indicators of Compromise

• Unexpected crashes in applications utilizing GNU Binutils demangling functions
• Stack overflow or segmentation fault errors in processes handling binary analysis or debugging
• Repeated application restarts when processing specific binary files or symbol data

Detection Strategies

• Monitor for abnormal process termination patterns in applications using GNU Binutils libraries
• Implement file integrity monitoring for binutils components to detect unauthorized modifications
• Deploy application crash analysis tools to identify stack overflow patterns indicative of exploitation attempts

Monitoring Recommendations

• Enable core dump analysis for applications processing untrusted binary files
• Implement logging for demangling operations that process external or user-provided data
• Set up alerts for repeated application crashes involving libiberty or related GNU Binutils components

How to Mitigate CVE-2021-32256

Immediate Actions Required

• Upgrade GNU Binutils to a patched version newer than 2.36
• Restrict processing of untrusted binary files or symbol data until patches are applied
• Implement input validation for any user-provided data that undergoes symbol demangling

Patch Information

The vulnerability affects GNU Binutils version 2.36. Users should upgrade to a newer version of GNU Binutils that includes the fix for this stack overflow issue. Review the Launchpad Bug Report for distribution-specific patch information. Additional vendor guidance is available in the NetApp Security Advisory.

Workarounds

• Avoid processing binary files or symbol data from untrusted sources
• Implement process sandboxing or resource limits (ulimit) to contain stack overflow impacts
• Use alternative demangling tools that are not affected by this vulnerability when processing untrusted input

# Configuration example: Set stack size limits to mitigate impact
ulimit -s 8192

# Alternatively, use systemd service limits
# Add to service unit file:
# [Service]
# LimitSTACK=8388608