CVE-2023-26554: NTP Buffer Overflow Vulnerability

CVE-2023-26554 Overview

CVE-2023-26554 is an out-of-bounds write vulnerability discovered in the mstolfp function within libntp/mstolfp.c in NTP version 4.2.8p15. The vulnerability occurs when the function adds a null terminator character (\0) during string processing, potentially writing beyond allocated buffer boundaries. An adversary may be able to exploit this flaw to attack client ntpq processes, though the vulnerability does not affect the ntpd daemon directly.

Critical Impact

Successful exploitation could allow an attacker to compromise NTP client query tools (ntpq), potentially leading to memory corruption, information disclosure, or denial of service conditions on systems running the vulnerable NTP version.

Affected Products

• NTP version 4.2.8p15
• Systems running ntpq client from the affected NTP package
• Linux, Unix, and BSD distributions shipping NTP 4.2.8p15

Discovery Timeline

• 2023-04-11 - CVE-2023-26554 published to NVD
• 2025-02-11 - Last updated in NVD database

Technical Details for CVE-2023-26554

Vulnerability Analysis

This out-of-bounds write vulnerability (CWE-787) exists in the mstolfp function, which is responsible for converting millisecond timestamps to NTP's internal long floating-point format. The flaw occurs during string manipulation when the function appends a null terminator character without properly validating buffer boundaries.

The attack requires network access and involves some complexity, as the adversary must craft specific input that triggers the vulnerable code path. While the vulnerability is exploitable remotely, it specifically affects the ntpq client process rather than the main ntpd daemon. This limitation means that time synchronization services remain unaffected, but client-side query operations could be compromised.

The potential impact includes partial compromise of confidentiality, integrity, and availability of the affected ntpq process, which could lead to information leakage, memory corruption, or process crashes.

Root Cause

The root cause of CVE-2023-26554 lies in improper bounds checking within the mstolfp function in libntp/mstolfp.c. When processing input strings and appending the null terminator character, the function fails to verify that sufficient buffer space exists for the additional character. This oversight allows writing beyond the allocated buffer boundaries, resulting in an out-of-bounds write condition.

Attack Vector

The vulnerability is exploitable over the network, though with high attack complexity. An attacker would need to interact with a vulnerable ntpq client process by providing specially crafted input that triggers the mstolfp function to perform the out-of-bounds write. The attack does not require any privileges or user interaction, but the specific conditions needed to successfully exploit the vulnerability increase the difficulty of a successful attack.

The attack is limited to client-side ntpq processes, meaning attackers cannot directly compromise the ntpd daemon that handles time synchronization. This architectural separation provides some protection for critical NTP server functionality.

The vulnerability mechanism involves the mstolfp function improperly handling buffer boundaries when adding a null terminator character during string processing. Technical details and analysis can be found in the GitHub CVE-2023-26554 Listing.

Detection Methods for CVE-2023-26554

Indicators of Compromise

• Unexpected crashes or segmentation faults in ntpq client processes
• Anomalous memory access patterns in NTP-related processes
• Core dumps containing evidence of buffer overflows in libntp components
• Unusual network traffic targeting NTP client query interfaces

Detection Strategies

• Monitor for abnormal ntpq process behavior including unexpected terminations or restarts
• Implement memory corruption detection tools (AddressSanitizer, Valgrind) in development and testing environments
• Review system logs for NTP client process crashes or error conditions
• Deploy network monitoring to detect malformed NTP-related traffic patterns

Monitoring Recommendations

• Enable process monitoring for ntpq client applications on systems running NTP 4.2.8p15
• Configure crash reporting and core dump analysis to capture potential exploitation attempts
• Implement endpoint detection capabilities to identify memory corruption exploitation patterns
• Monitor network traffic for suspicious connections to systems running vulnerable NTP versions

How to Mitigate CVE-2023-26554

Immediate Actions Required

• Identify all systems running NTP version 4.2.8p15 and prioritize them for updates
• Update to a patched version of NTP when available from your distribution vendor
• Limit network exposure of systems running vulnerable NTP client tools
• Restrict access to ntpq functionality to trusted administrators only

Patch Information

Organizations should check with their operating system vendor for patched versions of NTP that address CVE-2023-26554. Additional technical information and discussion regarding this vulnerability can be found in the GitHub Issue Discussion #1. Apply vendor-provided patches as they become available through standard package management systems.

Workarounds

• Restrict network access to systems running ntpq using firewall rules
• Consider using alternative NTP implementations such as chrony or systemd-timesyncd where applicable
• Disable or limit access to ntpq functionality on systems where it is not required
• Implement network segmentation to isolate NTP client systems from untrusted networks

# Configuration example
# Restrict ntpq access via firewall rules (iptables example)
iptables -A INPUT -p udp --dport 123 -s trusted_network_cidr -j ACCEPT
iptables -A INPUT -p udp --dport 123 -j DROP

# Verify NTP version on your system
ntpq --version