CVE-2020-1751: GNU Glibc DOS Vulnerability

CVE-2020-1751 Overview

An out-of-bounds write vulnerability was discovered in GNU glibc before version 2.31 when handling signal trampolines on PowerPC architecture. The vulnerability exists in the backtrace function, which fails to properly validate array bounds when storing frame addresses during stack unwinding operations. This memory corruption flaw can result in denial of service conditions or potentially enable arbitrary code execution on affected systems.

Critical Impact

Local attackers with low privileges can exploit this out-of-bounds write vulnerability to crash applications or potentially execute arbitrary code on PowerPC systems running vulnerable glibc versions.

Affected Products

• GNU glibc versions before 2.31
• Red Hat Enterprise Linux 8.0
• Canonical Ubuntu Linux 16.04 ESM, 18.04 LTS, and 19.10

Discovery Timeline

• 2020-04-17 - CVE-2020-1751 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-1751

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write) and affects the GNU C Library's signal handling mechanism specifically on PowerPC platforms. The flaw resides in how the backtrace() function processes signal trampolines—special code sequences used to handle signal delivery and return.

When a signal is delivered to a process on PowerPC, the kernel sets up a signal trampoline on the stack. The backtrace() function attempts to unwind the stack to capture the call chain, but it fails to properly validate the boundaries of the destination array when storing frame addresses. This allows an attacker to craft conditions where the function writes beyond the allocated buffer, corrupting adjacent memory regions.

The vulnerability requires local access with low privileges to exploit, though the attack complexity is high due to the need to manipulate signal delivery timing and stack layout on PowerPC systems. Successful exploitation can compromise confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause stems from insufficient bounds checking in the backtrace() function implementation for PowerPC architecture. When traversing the stack frames during signal trampoline processing, the function stores frame addresses without verifying that the array index remains within the allocated bounds. This oversight allows writes to memory locations outside the intended buffer when processing specially crafted or malformed signal contexts.

Attack Vector

The attack vector is local, requiring an authenticated user with low-level privileges on a PowerPC-based system. An attacker would need to:

1. Trigger signal delivery to a target process using vulnerable glibc
2. Manipulate the signal context or stack layout to create conditions where backtrace() is invoked
3. Cause the function to exceed array bounds during frame address storage
4. Leverage the out-of-bounds write to corrupt critical memory structures

The vulnerability mechanism involves improper array bounds validation during stack frame traversal in signal trampoline handling. For detailed technical analysis, refer to the Sourceware Bug Report #25423 which documents the specific code paths involved.

Detection Methods for CVE-2020-1751

Indicators of Compromise

• Unexpected application crashes or segmentation faults on PowerPC systems, particularly in processes using backtrace() functionality
• Core dumps showing memory corruption near signal handler stack frames
• Anomalous signal delivery patterns to processes running glibc-based applications
• Stack traces indicating corruption in the backtrace() or signal handling code paths

Detection Strategies

• Monitor system logs for repeated crashes in applications linked against vulnerable glibc versions on PowerPC architecture
• Implement memory corruption detection tools such as AddressSanitizer during development and testing phases
• Deploy runtime protection mechanisms that detect out-of-bounds memory access patterns
• Use SentinelOne's behavioral AI to identify exploitation attempts targeting memory corruption vulnerabilities

Monitoring Recommendations

• Enable core dump collection and analysis for applications on PowerPC systems to identify potential exploitation attempts
• Monitor for unusual signal delivery patterns using audit frameworks
• Track glibc version inventory across PowerPC infrastructure to ensure vulnerable versions are identified
• Implement file integrity monitoring on glibc libraries to detect unauthorized modifications

How to Mitigate CVE-2020-1751

Immediate Actions Required

• Upgrade GNU glibc to version 2.31 or later on all affected PowerPC systems
• Apply vendor-specific security patches from Red Hat, Canonical, or Gentoo as appropriate for your distribution
• Prioritize patching PowerPC-based infrastructure where this vulnerability is exploitable
• Review and restrict local access privileges to minimize the attack surface

Patch Information

Security patches addressing this vulnerability are available from multiple vendors:

• Red Hat: Refer to Red Hat Bug Report CVE-2020-1751 for Enterprise Linux patches
• Ubuntu: Apply updates from Ubuntu USN-4416-1 Advisory for affected Ubuntu versions
• Gentoo: Follow remediation guidance in Gentoo GLSA 202006-04 Advisory
• NetApp: Consult NetApp Security Advisory NTAP-20200430-0002 for affected NetApp products

Workarounds

• Restrict local user access on PowerPC systems to reduce the pool of potential attackers
• Implement application-level sandboxing to contain the impact of potential exploitation
• Monitor and limit the use of backtrace() functionality in critical applications where feasible
• Deploy defense-in-depth measures including ASLR and stack canaries to complicate exploitation

# Check installed glibc version on Linux systems
ldd --version

# Update glibc on Red Hat/CentOS systems
sudo yum update glibc

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

# Verify the update was applied
ldd --version | head -1