CVE-2023-22809: Sudo Privilege Escalation Vulnerability

CVE-2023-22809 Overview

CVE-2023-22809 is a privilege escalation vulnerability in Sudo's sudoedit (also known as sudo -e) feature that affects versions 1.8.0 through 1.9.12p1. The vulnerability stems from improper handling of extra arguments passed through user-controlled environment variables (SUDO_EDITOR, VISUAL, and EDITOR). A local attacker with sudo privileges to run sudoedit can exploit this flaw to append arbitrary files to the list of files being edited, potentially allowing them to modify sensitive system files and escalate privileges to root.

Critical Impact

Local attackers can leverage sudoedit permissions to edit arbitrary files on the system, potentially overwriting critical configuration files like /etc/sudoers or /etc/shadow to achieve full root access.

Affected Products

• Sudo Project Sudo versions 1.8.0 through 1.9.12p1
• Debian Linux 10.0 and 11.0
• Fedora 36 and 37
• Apple macOS (multiple versions)

Discovery Timeline

• 2023-01-18 - CVE CVE-2023-22809 published to NVD
• 2025-04-04 - Last updated in NVD database

Technical Details for CVE-2023-22809

Vulnerability Analysis

The sudoedit feature in Sudo is designed to allow users to safely edit files with elevated privileges without granting full shell access. When sudoedit is invoked, it copies the target file to a temporary location, allows the user to edit it with their preferred editor (determined by environment variables), and then copies the modified file back to the original location.

The vulnerability exists in how sudoedit parses the editor command specified in environment variables. The code intended to prevent users from passing additional arguments to the editor by looking for spaces and quotes, but it failed to account for the -- argument separator convention used by POSIX-compliant programs. By crafting a malicious editor string containing -- followed by additional file paths, an attacker can inject arbitrary files into the list of files that sudoedit will process.

When a user has permission to edit specific files via sudoedit, they can exploit this flaw to also edit files they were never intended to access. This completely bypasses the security model that sudoedit was designed to enforce.

Root Cause

The root cause is improper input validation in the argument parsing logic for user-specified editor commands. The protection mechanism that was supposed to prevent additional arguments from being passed to the editor did not account for the -- end-of-options marker. This allowed attackers to use a carefully crafted EDITOR, VISUAL, or SUDO_EDITOR environment variable value to inject additional file paths that would be processed alongside the intended target file.

Attack Vector

The attack requires local access to a system where the attacker has permission to use sudoedit for at least one file. The attacker sets one of the editor environment variables (SUDO_EDITOR, VISUAL, or EDITOR) to include the -- argument followed by the path to a sensitive file they want to modify.

For example, if a user is granted sudoedit access to /etc/custom.conf, they can set their editor environment variable to include additional files like /etc/sudoers. When sudoedit runs, it processes both the permitted file and the injected file, allowing the attacker to grant themselves full sudo access.

The exploitation flow involves:

1. Identifying a sudoedit permission granted to the attacker's user
2. Setting the EDITOR or similar environment variable to include -- /path/to/sensitive/file
3. Running sudoedit against the permitted file
4. The editor opens both the permitted file and the injected sensitive file
5. Modifying the sensitive file to escalate privileges (e.g., adding the attacker to sudoers)

Detection Methods for CVE-2023-22809

Indicators of Compromise

• Unexpected modifications to system configuration files such as /etc/sudoers, /etc/passwd, or /etc/shadow
• Audit logs showing sudoedit execution with unusual editor environment variable values containing --
• New unauthorized entries in /etc/sudoers or /etc/sudoers.d/ directory
• Timestamp anomalies on critical system files that should not have been modified

Detection Strategies

• Monitor process execution for sudoedit commands where the EDITOR, VISUAL, or SUDO_EDITOR environment variables contain the -- string followed by file paths
• Implement file integrity monitoring on critical system files including /etc/sudoers, /etc/passwd, /etc/shadow, and SSH authorized_keys files
• Configure audit rules to log all sudoedit executions and capture associated environment variables
• Deploy SentinelOne endpoint protection to detect privilege escalation attempts and unauthorized file modifications

Monitoring Recommendations

• Enable comprehensive auditd logging for sudo and sudoedit command execution with environment variable capture
• Implement real-time alerting on modifications to privileged configuration files
• Review sudo logs regularly for patterns indicating exploitation attempts
• Monitor for new user accounts or permission changes that could indicate successful privilege escalation

How to Mitigate CVE-2023-22809

Immediate Actions Required

• Upgrade Sudo to version 1.9.12p2 or later immediately on all affected systems
• Review sudoers configuration to identify all users with sudoedit permissions
• Audit recent modifications to sensitive system files for signs of exploitation
• Consider temporarily removing sudoedit permissions until patches are applied

Patch Information

The Sudo Project has released version 1.9.12p2 which addresses this vulnerability. Organizations should update to this version or later through their distribution's package manager. Security patches are also available from major Linux distributions including Debian (DSA-5321), Fedora, and Gentoo (GLSA 202305-12). Apple has addressed this vulnerability in macOS updates documented in HT213758.

For detailed patch information, refer to the Sudo Security Advisory and the Synacktiv technical analysis.

Workarounds

• Remove sudoedit (or sudo -e) permissions from users where possible until patching is complete
• Use the NOEXEC tag in sudoers to prevent shell escapes, though this does not fully mitigate the vulnerability
• Restrict the env_editor option by setting Defaults !env_editor in sudoers to disable user-controlled editor variables
• Implement strict file integrity monitoring as a compensating control

# Disable user-controlled editor environment variables in sudoers
# Add to /etc/sudoers or /etc/sudoers.d/security
Defaults !env_editor
Defaults editor="/usr/bin/vi"