CVE-2021-43618: Gmplib GMP Buffer Overflow Vulnerability

CVE-2021-43618 Overview

GNU Multiple Precision Arithmetic Library (GMP) through version 6.2.1 contains an integer overflow vulnerability in mpz/inp_raw.c that results in a buffer overflow when processing crafted input. This vulnerability leads to a segmentation fault, primarily affecting 32-bit platforms. The GMP library is widely used for arbitrary precision arithmetic operations and is a dependency for numerous cryptographic and mathematical applications.

Critical Impact

This integer overflow vulnerability can cause denial of service through application crashes on systems using affected versions of the GMP library. 32-bit platforms are particularly vulnerable to exploitation.

Affected Products

• GMP Library through version 6.2.1 (32-bit platforms)
• Debian Linux 9.0
• NetApp Active IQ Unified Manager for VMware vSphere
• NetApp H300S, H500S, H700S, H410S, and H410C firmware

Discovery Timeline

• November 15, 2021 - CVE-2021-43618 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2021-43618

Vulnerability Analysis

This vulnerability exists in the mpz/inp_raw.c file of the GNU Multiple Precision Arithmetic Library. The flaw occurs during the processing of input data where an integer overflow condition can be triggered. When a specially crafted input is processed, the integer overflow leads to an incorrect buffer size calculation, subsequently causing a buffer overflow condition.

The vulnerability specifically affects 32-bit platforms due to the integer size limitations inherent to these architectures. On 32-bit systems, the maximum representable integer value is significantly smaller than on 64-bit systems, making overflow conditions more likely to occur when processing large or maliciously crafted values.

Root Cause

The root cause is an Integer Overflow (CWE-190) vulnerability in the input processing routine within mpz/inp_raw.c. The code fails to properly validate input values before performing arithmetic operations, allowing attackers to supply values that exceed the maximum integer representation, wrapping around to small values and causing subsequent buffer allocation errors.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by sending specially crafted input to an application that uses the GMP library for processing. When the vulnerable mpz_inp_raw() function parses this malicious input, the integer overflow occurs, leading to a buffer overflow and subsequent segmentation fault.

The exploitation mechanism involves:

1. Crafting input data with values designed to trigger integer overflow during size calculations
2. Sending this data to an application utilizing the GMP library
3. The integer overflow causes incorrect memory allocation
4. A buffer overflow occurs when data is written beyond the allocated memory boundaries
5. The application crashes with a segmentation fault, resulting in denial of service

Detection Methods for CVE-2021-43618

Indicators of Compromise

• Application crashes with segmentation faults in processes utilizing the GMP library
• Abnormal memory allocation patterns in applications performing arbitrary precision arithmetic
• Unexpected termination of services that depend on GMP for cryptographic operations
• Core dumps indicating memory access violations in mpz/inp_raw.c related functions

Detection Strategies

• Monitor for segmentation fault signals (SIGSEGV) in applications linked against GMP library versions prior to the fix
• Implement input validation monitoring for applications processing external mathematical data
• Deploy application-level monitoring to detect unusual crash patterns in GMP-dependent services
• Use memory sanitizers during development and testing to identify potential overflow conditions

Monitoring Recommendations

• Enable detailed logging for applications using GMP library to capture crash events and stack traces
• Implement process monitoring to detect and alert on unexpected application terminations
• Review system logs for patterns indicating denial of service attempts targeting mathematical processing functions
• Monitor network traffic for anomalous input patterns to services utilizing GMP for data processing

How to Mitigate CVE-2021-43618

Immediate Actions Required

• Update the GMP library to a patched version that addresses the integer overflow in mpz/inp_raw.c
• Prioritize patching on 32-bit systems which are most vulnerable to this exploitation
• Review all applications that depend on GMP and ensure they are using updated library versions
• Consider migrating critical applications from 32-bit to 64-bit platforms where feasible

Patch Information

The GMP project has released a fix for this vulnerability. The patch is available in the GMP 6.2 repository at commit 561a9c25298e. Distribution-specific patches are also available:

• Debian LTS Advisory for Debian 9.0
• Gentoo GLSA 2023-09-13 for Gentoo Linux
• NetApp Security Advisory NTAP-20221111-0001 for affected NetApp products

Additional technical details can be found in the Debian Bug Report #994405 and the GMP Bug Mailing List.

Workarounds

• Implement input size validation before passing data to GMP library functions
• Deploy application-level firewalls to filter potentially malicious mathematical input
• Restrict network access to services utilizing the GMP library to trusted sources only
• Consider implementing process isolation for applications dependent on GMP to limit the impact of crashes

# Check installed GMP version and update on Debian-based systems
dpkg -l libgmp*
apt-get update && apt-get upgrade libgmp10

# Verify the update
dpkg -l libgmp* | grep -E "^ii"