CVE-2023-4641: Shadow-utils Information Disclosure Flaw

CVE-2023-4641 Overview

A memory information disclosure vulnerability has been identified in shadow-utils, a collection of password and account management tools widely used in Linux distributions. When shadow-utils prompts for a new password, it requests the password twice for confirmation. If the password entry fails on the second attempt, the utility fails to properly clean the memory buffer that stored the first password entry. This improper handling leaves sensitive password data exposed in memory, potentially allowing an attacker with local access to retrieve plaintext passwords.

Critical Impact

Attackers with local system access could extract plaintext passwords from memory, leading to credential theft and potential privilege escalation across enterprise Linux environments.

Affected Products

• shadow-maint shadow-utils
• Red Hat Enterprise Linux 8.0 and 9.0 (including ARM64, IBM z Systems, and Power architectures)
• Red Hat CodeReady Linux Builder 8.0 and 9.0 (all supported architectures)

Discovery Timeline

• December 27, 2023 - CVE-2023-4641 published to NVD
• November 3, 2025 - Last updated in NVD database

Technical Details for CVE-2023-4641

Vulnerability Analysis

This vulnerability represents a classic memory information disclosure flaw (CWE-303: Incorrect Implementation of Authentication Algorithm, CWE-287: Improper Authentication). The core issue resides in the password change workflow within shadow-utils utilities such as passwd and related tools.

When a user initiates a password change operation, the utility follows a standard security practice of requesting the new password twice to confirm the user's intent and prevent typos. The first password entry is stored in a memory buffer while the user types the second confirmation entry. Under normal successful operation, both buffers would be securely zeroed after comparison.

However, when the second password entry fails validation (either due to mismatch with the first entry or other validation failures), the code path that handles this error condition does not properly sanitize the buffer containing the first password. This leaves plaintext password data residing in process memory after the operation completes.

Root Cause

The root cause is insufficient memory sanitization in the error handling path of the password confirmation routine. While the success path correctly clears sensitive buffers using secure memory erasure functions, the failure path bypasses this cleanup logic. This is a common pattern in security-sensitive code where developers focus on the happy path but overlook cleanup requirements in error conditions.

The vulnerability exists because the buffer clearing operation was conditionally executed only when password validation succeeded, rather than being placed in a cleanup block that executes regardless of the operation outcome.

Attack Vector

Exploitation requires local access to the system where shadow-utils is installed. An attacker would need sufficient privileges to read process memory, which could be achieved through various means:

The attacker must first gain local access to a system running affected versions of shadow-utils. Once positioned, they would wait for or trigger a password change operation by another user. After a failed password confirmation attempt occurs, the attacker can attempt to read the victim's process memory space.

Memory reading could be accomplished through debugging interfaces like /proc/[pid]/mem if the attacker has appropriate permissions, through exploitation of other vulnerabilities that grant memory access, or through physical access to system memory (cold boot attacks, memory forensics on compromised systems).

The attack window exists from when the password change fails until the process terminates or the memory is overwritten by subsequent operations.

Detection Methods for CVE-2023-4641

Indicators of Compromise

• Unusual access patterns to /proc/*/mem or /proc/*/maps files targeting passwd, chpasswd, or related shadow-utils processes
• Unexpected debugging activity on password-related processes using ptrace system calls
• Anomalous memory dump files or core dumps being created on the system
• Failed password change attempts followed by suspicious process attachment activity

Detection Strategies

• Monitor audit logs for ptrace system calls targeting shadow-utils binaries and related processes
• Implement file integrity monitoring on shadow-utils binaries to detect tampering or replacement
• Configure auditd rules to track access to password-related utilities and their process memory spaces
• Deploy endpoint detection to identify memory scraping tools or techniques targeting authentication processes

Monitoring Recommendations

• Enable comprehensive audit logging for authentication-related events using auditd with rules targeting execve calls to shadow-utils binaries
• Implement real-time alerting on suspicious combinations of failed password changes and subsequent memory access attempts
• Monitor for core dump generation in unusual contexts, as attackers may force crashes to capture memory contents
• Track user sessions for anomalous patterns around password change operations

How to Mitigate CVE-2023-4641

Immediate Actions Required

• Apply vendor-provided security patches from Red Hat (RHSA-2023:6632, RHSA-2023:7112, RHSA-2024:0417, RHSA-2024:2577) immediately
• Review and restrict local access permissions to minimize the pool of users who could potentially exploit this vulnerability
• Audit systems for signs of prior exploitation, particularly looking at memory access patterns around shadow-utils processes
• Consider implementing mandatory password change for users who may have changed passwords on unpatched systems

Patch Information

Red Hat has released security advisories addressing this vulnerability across multiple Enterprise Linux versions. Organizations should apply the appropriate patches based on their deployed architecture:

• Red Hat Security Advisory RHSA-2023:6632 - Initial patch release
• Red Hat Security Advisory RHSA-2023:7112 - Additional platform coverage
• Red Hat Security Advisory RHSA-2024:0417 - Extended support update
• Red Hat Security Advisory RHSA-2024:2577 - Latest cumulative fix

Debian users should refer to the Debian LTS Announcement for applicable updates.

Additional technical details are available in Red Hat Bugzilla Report #2215945 and the Red Hat CVE Analysis page.

Workarounds

• Restrict local shell access to trusted users only, minimizing the attack surface for memory-based exploits
• Implement kernel hardening features such as kernel.yama.ptrace_scope=2 to restrict ptrace capabilities
• Deploy additional access controls around password change operations during maintenance windows
• Consider using alternative authentication mechanisms (PAM modules, LDAP, etc.) that may not be affected while awaiting patches

# Restrict ptrace capabilities to prevent memory inspection attacks
echo "kernel.yama.ptrace_scope = 2" >> /etc/sysctl.d/99-security.conf
sysctl -p /etc/sysctl.d/99-security.conf

# Verify current patch level for shadow-utils
rpm -q shadow-utils --changelog | head -20