CVE-2020-1752: GNU Glibc Use-After-Free Vulnerability

CVE-2020-1752 Overview

CVE-2020-1752 is a use-after-free vulnerability discovered in GNU C Library (glibc) upstream version 2.14. The flaw exists in the way tilde expansion is handled within the glob function. Directory paths containing an initial tilde followed by a valid username are affected by this vulnerability. A local attacker could exploit this issue by creating a specially crafted path that, when processed by the glob function, could potentially lead to arbitrary code execution.

Critical Impact

Local attackers can achieve arbitrary code execution through memory corruption via specially crafted directory paths processed by the glibc glob function's tilde expansion feature.

Affected Products

• GNU glibc versions 2.14 through 2.31
• Canonical Ubuntu Linux 16.04 LTS, 18.04 LTS, 19.10
• Debian Linux 10.0
• NetApp Active IQ Unified Manager for VMware vSphere
• NetApp HCI Management Node
• NetApp SolidFire
• NetApp SteelStore Cloud Integrated Storage
• NetApp H410C Firmware

Discovery Timeline

• 2020-04-30 - CVE-2020-1752 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-1752

Vulnerability Analysis

This use-after-free vulnerability (CWE-416) affects the tilde expansion functionality within glibc's glob function. The vulnerability was introduced in glibc version 2.14 and remained present until it was fixed in version 2.32. The flaw occurs when processing directory paths that begin with a tilde character (~) followed by a valid username.

When the glob function performs tilde expansion, it resolves the ~username pattern to the corresponding user's home directory. During this process, memory management errors can lead to a use-after-free condition, where the application continues to reference memory that has already been deallocated. This creates an opportunity for attackers to manipulate the freed memory region and potentially achieve arbitrary code execution.

The attack requires local access and user interaction, as an attacker must craft a malicious path and entice a victim or application to process it through the vulnerable glob function. Despite these requirements, successful exploitation could result in complete compromise of confidentiality, integrity, and availability on the affected system.

Root Cause

The root cause of CVE-2020-1752 lies in improper memory lifecycle management within the tilde expansion code path of glibc's glob function. When processing paths with tilde prefixes, the function allocates memory to store the expanded path. Due to a logic error introduced in version 2.14, this memory can be freed prematurely while still being referenced by other parts of the code. Subsequent access to this freed memory constitutes the use-after-free condition.

The specific fix was implemented in glibc version 2.32, addressing the memory management sequence to ensure proper allocation and deallocation timing during tilde expansion operations.

Attack Vector

The attack vector for CVE-2020-1752 is local, requiring the attacker to have some level of access to the target system. The exploitation scenario involves:

1. An attacker creates a specially crafted directory path containing a tilde followed by a valid username on the system
2. An application or user action triggers the glob function to process this malicious path
3. During tilde expansion, the use-after-free condition is triggered
4. The attacker leverages control over the freed memory region to redirect execution flow
5. Arbitrary code execution is achieved within the context of the vulnerable application

The technical details of exploitation involve controlling the contents of the freed memory region between the free operation and subsequent use. Attackers typically accomplish this through heap manipulation techniques such as heap spraying or precise timing of allocations.

For detailed technical analysis, refer to Sourceware Bug #25414 and the glibc Git Commit Reference.

Detection Methods for CVE-2020-1752

Indicators of Compromise

• Unusual directory paths containing tilde characters followed by usernames in application logs
• Unexpected crashes or memory corruption errors in applications utilizing the glob function
• Anomalous process behavior following path resolution operations
• Memory access violations originating from glibc functions

Detection Strategies

• Monitor system calls and library function invocations for suspicious glob function usage patterns
• Implement application-level logging for path expansion operations
• Deploy memory corruption detection tools such as AddressSanitizer during development and testing phases
• Use intrusion detection systems configured to identify exploitation attempts targeting memory corruption vulnerabilities

Monitoring Recommendations

• Enable detailed logging for applications that process user-supplied file paths
• Monitor for unusual patterns in home directory resolution requests
• Implement file integrity monitoring on critical system directories
• Deploy endpoint detection and response (EDR) solutions capable of detecting use-after-free exploitation techniques

How to Mitigate CVE-2020-1752

Immediate Actions Required

• Update glibc to version 2.32 or later immediately on all affected systems
• Prioritize patching systems running Ubuntu 16.04 LTS, 18.04 LTS, 19.10, and Debian 10.0
• Review and update NetApp products according to the NetApp Security Advisory
• Audit applications that use the glob function with user-supplied input

Patch Information

The vulnerability was fixed in glibc version 2.32. Organizations should apply vendor-specific patches based on their distribution:

• Ubuntu: Apply updates from Ubuntu USN-4416-1
• Debian: Follow guidance from the Debian LTS Announcement
• Gentoo: Apply Gentoo GLSA 202101-20
• NetApp: Refer to NetApp Security Advisory ntap-20200511-0005
• General: Consult Red Hat CVE-2020-1752 Bug for additional technical details

Workarounds

• Restrict local user access to minimize the attack surface for local exploitation
• Implement input validation for applications processing file paths with tilde expansion
• Deploy application sandboxing to limit the impact of potential code execution
• Use SELinux or AppArmor policies to constrain application capabilities

# Verify glibc version on affected systems
ldd --version

# Check for available glibc updates (Debian/Ubuntu)
apt-get update && apt-cache policy libc6

# Apply security updates (Debian/Ubuntu)
apt-get update && apt-get upgrade libc6

# For Red Hat/CentOS systems
yum update glibc