CVE-2023-42465: Sudo Authentication Bypass Vulnerability

CVE-2023-42465 Overview

CVE-2023-42465 is a vulnerability in Sudo versions prior to 1.9.15 that could allow row hammer attacks to bypass authentication or achieve privilege escalation. The vulnerability exists because the application logic in Sudo's authentication mechanisms is based on checking whether return values do not equal an error value, rather than explicitly verifying they equal a success value. This design flaw, combined with the use of values that do not resist single-bit flips, makes the authentication process susceptible to hardware-based row hammer attacks.

Row hammer attacks exploit physical characteristics of modern DRAM to cause bit flips in adjacent memory rows through repeated memory accesses. When applied to Sudo's authentication logic, an attacker could potentially flip a single bit in the authentication result variable, transforming a failure condition into a success condition.

Critical Impact

Local attackers with low privileges could potentially bypass sudo authentication or escalate privileges through hardware-based row hammer attacks targeting authentication return values.

Affected Products

• Sudo versions prior to 1.9.15
• Systems using Sudo for privilege escalation
• Linux and Unix-like operating systems with vulnerable Sudo installations

Discovery Timeline

• 2023-12-22 - CVE-2023-42465 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-42465

Vulnerability Analysis

The vulnerability stems from a fundamental design issue in how Sudo's authentication subsystem validates the success or failure of authentication attempts. The code compares return values against error constants (checking != AUTH_FAILURE) rather than explicitly verifying success (== AUTH_SUCCESS). This negative logic pattern creates a critical weakness: if an attacker can induce a single-bit flip in memory containing the authentication result variable through row hammer techniques, they could potentially change an authentication failure into an apparent success.

Row hammer attacks work by rapidly accessing the same memory row, causing electrical disturbance that can flip bits in physically adjacent rows. The practical exploitability depends on hardware characteristics, memory layout, and the attacker's ability to influence memory allocation patterns. The attack requires local access and the ability to execute code that triggers sufficient memory accesses.

Root Cause

The root cause is the use of negative authentication logic combined with values that are susceptible to single-bit manipulation. When authentication functions check if a return value does not equal an error code rather than explicitly checking for a success code, any unexpected value (including those caused by bit flips) may be interpreted as success. The authentication status variables were not designed with bit-flip resistance in mind.

Attack Vector

The attack requires local access to the target system. An attacker with low-privilege access would need to:

1. Identify memory regions used by Sudo's authentication variables
2. Execute row hammer sequences to induce bit flips in adjacent memory
3. Time the attack to coincide with an authentication attempt
4. Exploit the resulting bit flip to bypass authentication checks

The following patch from the Sudo project demonstrates the vulnerable pattern and its fix in plugins/sudoers/auth/passwd.c:

     char des_pass[9], *epass;
     char *pw_epasswd = auth->data;
     size_t pw_len;
-    int matched = 0;
+    int ret;
     debug_decl(sudo_passwd_verify, SUDOERS_DEBUG_AUTH);

     /* An empty plain-text password must match an empty encrypted password. */

Source: GitHub Commit for Sudo Project

The authentication flow was also updated in plugins/sudoers/auth/sudo_auth.c to use explicit success checking:

 	if (auth->init && !IS_DISABLED(auth)) {
 	    /* Disable if it failed to init unless there was a fatal error. */
 	    status = (auth->init)(ctx, pw, auth);
-	    if (status == AUTH_FAILURE)
+	    switch (status) {
+	    case AUTH_SUCCESS:
+		break;
+	    case AUTH_FAILURE:
 		SET(auth->flags, FLAG_DISABLED);
-	    else if (status == AUTH_ERROR)
-		break;		/* assume error msg already printed */
+		break;
+	    default:
+		/* Assume error msg already printed. */
+		debug_return_int(-1);
+	    }
 	}
     }

Source: GitHub Commit for Sudo Project

Detection Methods for CVE-2023-42465

Indicators of Compromise

• Unusual memory access patterns indicative of row hammer attempts
• Unexpected successful sudo authentication events from unauthorized users
• Abnormal privilege escalation activities without corresponding valid authentication
• High-frequency memory access operations prior to sudo invocations

Detection Strategies

• Monitor for processes exhibiting memory access patterns consistent with row hammer attacks
• Implement audit logging for all sudo authentication attempts and correlate with system behavior
• Use hardware-based memory integrity checking where available (ECC memory can mitigate some bit-flip attacks)
• Deploy file integrity monitoring on sudo binaries and configuration files

Monitoring Recommendations

• Enable comprehensive sudo logging via sudoers configuration directives
• Implement real-time alerting on authentication anomalies in centralized logging systems
• Monitor for unusual patterns of failed authentication followed by unexpected successes
• Track process behavior for memory thrashing patterns that could indicate exploitation attempts

How to Mitigate CVE-2023-42465

Immediate Actions Required

• Upgrade Sudo to version 1.9.15 or later immediately
• Audit systems for signs of unauthorized privilege escalation
• Review sudo logs for suspicious authentication patterns
• Consider deploying ECC memory on critical systems to reduce row hammer effectiveness

Patch Information

The Sudo project has released version 1.9.15 which addresses this vulnerability by changing the authentication logic to explicitly check for success values rather than checking for the absence of failure values. The patch modifies multiple authentication modules to use a switch statement pattern that handles AUTH_SUCCESS, AUTH_FAILURE, and treats any other value as an error condition.

Patches are available from the Sudo Project Release Notes. Additional security advisories have been published by Fedora, Gentoo, and NetApp.

Workarounds

• Deploy ECC (Error-Correcting Code) memory to detect and correct single-bit errors caused by row hammer
• Limit local access to systems running vulnerable Sudo versions
• Implement additional authentication layers beyond sudo where possible
• Consider kernel-level mitigations for row hammer attacks if available for your platform

# Check current sudo version
sudo --version

# Update sudo on Debian/Ubuntu
sudo apt update && sudo apt install sudo

# Update sudo on RHEL/CentOS/Fedora
sudo dnf update sudo

# Update sudo on Arch Linux
sudo pacman -Syu sudo