CVE-2020-10029: GNU Glibc Buffer Overflow Vulnerability

CVE-2020-10029 Overview

CVE-2020-10029 is a stack buffer overflow vulnerability in the GNU C Library (glibc) before version 2.32. The vulnerability occurs during range reduction when an input to an 80-bit long double function contains a non-canonical bit pattern. This flaw is specifically triggered when passing specially crafted values (such as 0x5d414141414141410000) to functions like sinl on x86 targets. The vulnerability is related to the sysdeps/ieee754/ldbl-96/e_rem_pio2l.c file in the glibc source code.

Critical Impact

Local attackers can cause denial of service through stack buffer overflow by providing malformed 80-bit long double values to mathematical functions, potentially crashing applications that rely on glibc.

Affected Products

• GNU glibc (versions before 2.32)
• Fedora 30, 31, and 32
• Canonical Ubuntu Linux 16.04 ESM, 18.04 LTS, and 19.10
• openSUSE Leap 15.1
• NetApp Active IQ Unified Manager, Cloud Backup, HCI Management Node, SolidFire, and SteelStore Cloud Integrated Storage
• NetApp H410C (firmware and hardware)
• Debian Linux 10.0

Discovery Timeline

• March 4, 2020 - CVE-2020-10029 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-10029

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), specifically a stack buffer overflow condition. The flaw exists in the range reduction algorithm used by 80-bit long double trigonometric functions in glibc. When processing floating-point values with non-canonical bit patterns—values that do not conform to the expected IEEE 754 extended precision format—the e_rem_pio2l.c implementation fails to properly validate input boundaries, resulting in a write operation that exceeds the allocated stack buffer.

The vulnerability requires local access to exploit, as an attacker must be able to pass a crafted floating-point value to an affected function. While this limits the attack surface, any application using glibc's long double mathematical functions (such as sinl, cosl, tanl, and related functions) on x86 architectures is potentially vulnerable. The impact is primarily denial of service through application crash, though stack corruption could theoretically lead to more severe consequences depending on the application context.

Root Cause

The root cause lies in the e_rem_pio2l.c file within the sysdeps/ieee754/ldbl-96/ directory. The range reduction algorithm in this file processes 80-bit long double values to reduce them to a range suitable for accurate trigonometric calculations. However, the code does not properly handle non-canonical bit patterns in the input—specifically, values where the explicit integer bit (bit 63) does not match the expected value for the given exponent.

When a non-canonical value like 0x5d414141414141410000 is passed to functions like sinl, the range reduction logic miscalculates buffer requirements, leading to an on-stack buffer overflow. This occurs because the algorithm's assumptions about input value ranges are violated by the malformed bit pattern.

Attack Vector

The attack requires local access to the target system. An attacker must be able to invoke a vulnerable glibc mathematical function (such as sinl, cosl, or tanl) with a specially crafted 80-bit long double value containing non-canonical bit patterns. This could be achieved through:

1. Direct invocation in a local application context
2. Providing malformed input to an application that processes floating-point values and passes them to trigonometric functions
3. Exploiting applications that accept user-controlled floating-point data without proper validation

The non-canonical bit pattern 0x5d414141414141410000 demonstrates the attack, where the explicit integer bit conflicts with the exponent field, triggering the overflow condition during the range reduction phase of the sinl function.

Detection Methods for CVE-2020-10029

Indicators of Compromise

• Unexpected application crashes or segmentation faults in processes using glibc mathematical functions
• Core dumps showing stack corruption in e_rem_pio2l.c or related trigonometric function call stacks
• System logs indicating abnormal termination of applications using sinl, cosl, tanl, or similar long double functions

Detection Strategies

• Monitor for segmentation faults and abnormal process terminations in applications that perform trigonometric calculations
• Implement application-level input validation to reject non-canonical floating-point bit patterns before passing values to glibc functions
• Use AddressSanitizer (ASAN) or similar memory debugging tools in development environments to detect stack buffer overflows
• Deploy endpoint detection solutions capable of identifying memory corruption patterns characteristic of buffer overflow attacks

Monitoring Recommendations

• Enable crash dump collection and analysis for applications using glibc mathematical libraries
• Implement logging for applications that process external floating-point input data
• Monitor system stability metrics for unexpected increases in application crashes or restarts
• Review security advisories from distribution vendors (Fedora Package Announcement, Ubuntu Security Notice, Debian LTS Security Notice)

How to Mitigate CVE-2020-10029

Immediate Actions Required

• Update glibc to version 2.32 or later where the vulnerability has been patched
• Apply distribution-specific security updates from your Linux vendor
• Identify all systems running vulnerable glibc versions using package management tools (rpm -qa | grep glibc or dpkg -l | grep libc6)
• Prioritize updates for systems processing untrusted floating-point input

Patch Information

The vulnerability has been addressed in glibc version 2.32 and later. The fix is tracked in the Sourceware Bug Report, and the specific commit can be found in the glibc Commit Update.

Distribution-specific patches are available through:

• Ubuntu Security Notice USN-4416-1
• Gentoo GLSA 202006-04
• openSUSE Security Announcement
• NetApp Security Advisory

Workarounds

• Implement input validation at the application level to reject floating-point values with non-canonical bit patterns before they reach glibc functions
• Consider using alternative mathematical libraries for applications that cannot be immediately updated
• Restrict local access to systems running vulnerable glibc versions where possible
• For containerized environments, ensure base images are updated with patched glibc versions

# Check current glibc version
ldd --version

# Update glibc on Debian/Ubuntu systems
sudo apt update && sudo apt upgrade libc6

# Update glibc on RHEL/Fedora systems
sudo dnf update glibc

# Verify the update
ldd --version