External risk intelligence

Sudo Privilege Escalation Vulnerability

CVE advisoryKnown Exploit

CVE-2021-3156

A vulnerability in the sudo command allows any local user to gain root privileges. This could enable unauthorized data access and system control, posing a significant risk to organizational confidentiality and integrity.

1Halo Surface Signal

Privilege Escalation

Sudo Project Sudo

1.8.2 to before 1.8.321.9.0 to before 1.9.51.9.532339.010.098.2.179.2.810.0.43.06.2before 21.1.1before 10.3.2-10310400 to 4102105a610 to 65510.3.0.0.0 to 10....

External exposure likelihood

Halo Surface Signal score for CVE-2021-3156

This vulnerability is a local privilege escalation in the sudo utility. It requires the attacker to already have local access to the system and an existing user account to execute the vulnerable command, making it physically or locally constrained rather than reachable via the public internet.

Horizon Alert

Summary of the vulnerability and why it matters

The `sudo` program contains a flaw that can allow unauthorized access. This weakness could enable an attacker to gain elevated privileges on a system. Organizations could face risks associated with compromised systems and unauthorized data access.

Vulnerable component: `sudo` program
Core weakness: Buffer overflow error
Main business impact: Privilege escalation

Attack Path

How an attacker could exploit the issue

An attacker can exploit a vulnerability in the sudo command to escalate privileges on a system. This occurs when a specially crafted command-line argument is used with `sudoedit -s`. The system processes this argument, leading to a buffer overflow that allows the attacker to gain root-level control. This could allow an attacker to modify system files, install malicious software, or disrupt operations.

Local access required to start.
Triggered by `sudoedit -s` argument.
Attacker gains root control.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability allows for privilege escalation on affected systems, meaning an attacker could gain administrative control. The risk is significant due to the potential for unauthorized access and data compromise. Organizations should prioritize addressing this vulnerability to mitigate potential business impact.

Attackers with basic technical skills.
Local access to the system required.
High business risk and urgency.

Priority actions

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in sudo could allow an unauthorized user with local access to escalate their privileges to root. This could enable unauthorized actions and potentially impact the integrity and availability of affected systems and data. Organizations should prioritize understanding their exposure to this vulnerability.

Identify systems running the affected sudo versions.
Restrict or monitor sudoedit command usage.
Apply vendor updates and validate system integrity.

Frequently asked questions

What is sudo and what is it used for?

Sudo, which stands for "substitute user do" or "superuser do," is a command-line utility that allows permitted users to run programs with the security privileges of another user, typically the superuser or root. It's commonly used on Unix-like operating systems to grant temporary elevated permissions for specific administrative tasks without requiring users to log in as root directly.

How does CVE-2021-3156 work?

CVE-2021-3156 is a heap-based buffer overflow vulnerability, categorized as CWE-193 (Off-by-one Error). It occurs in sudo versions prior to 1.9.5p2. An attacker can exploit this by using the "sudoedit -s" command with a specific command-line argument that ends with a single backslash, leading to the overflow and potential privilege escalation.

What are the preconditions for exploiting CVE-2021-3156?

To exploit this vulnerability, an attacker must have local access to the affected system. They also need an existing user account on that system that has been granted sudo privileges. Running the "sudoedit -s" command with a specially crafted argument is the method of exploitation; however, a command-line argument that does not end with a single backslash will not trigger this specific vulnerability.

Who should be concerned about this sudo vulnerability (CVE-2021-3156)?

Organizations running sudo versions prior to 1.9.5p2 should be concerned. Based on the Halo Surface Signal, this vulnerability is classified as internal because it requires local access to the system, meaning it's not directly exploitable from the public internet but rather from within a compromised network or by an attacker with physical access.

What is the first step for addressing this sudo vulnerability?

The primary first step for anyone running affected versions of sudo is to update the software. Applying security patches and updates provided by the sudo project or your operating system vendor is crucial to mitigate this privilege escalation risk.

References

Written by Nicholas Merritt

External-surface CVE analysis and Halo Surface Signal prioritization for Halo Threat Intelligence.