CVE-2022-24903: Rsyslog Buffer Overflow Vulnerability

CVE-2022-24903 Overview

CVE-2022-24903 is a heap buffer overflow vulnerability affecting Rsyslog, the widely-used high-performance system logging utility. The vulnerability exists in modules responsible for TCP syslog reception when octet-counted framing is used. Successful exploitation can result in a segmentation fault or other system malfunctions, potentially impacting the integrity of logging infrastructure critical to security monitoring and incident response.

Critical Impact

This heap buffer overflow in Rsyslog's TCP syslog reception modules affects systems using octet-counted framing, potentially causing service disruption and memory corruption in critical logging infrastructure.

Affected Products

• Rsyslog rsyslog (all versions prior to the security patch)
• Fedora 35
• Debian Linux 9.0, 10.0, and 11.0
• NetApp Active IQ Unified Manager for VMware vSphere

Discovery Timeline

• 2022-05-06 - CVE-2022-24903 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-24903

Vulnerability Analysis

The vulnerability resides in the octet-counting framing implementation used by several Rsyslog TCP reception modules. The flaw occurs during the parsing of the octet count value that precedes syslog messages in this framing format. While the code includes validation to check for the maximum number of octets, the implementation contains a logic error where digits continue to be written to a heap buffer even after the octet count exceeds the maximum allowed value.

This buffer overrun condition can corrupt heap memory, leading to segmentation faults or other undefined behavior. The affected modules include imtcp, imptcp, imgssapi, and imhttp, which handle standard syslog message reception, as well as imdiag, a diagnostics module used primarily for testing.

The exploitation complexity is elevated because once the digit sequence terminates, no additional characters can be written to the buffer. This constraint significantly limits the attacker's ability to control the overflow content, making arbitrary code execution difficult though not definitively impossible according to the vendor assessment.

Root Cause

The root cause is an improper validation of input (CWE-1284) combined with a classic buffer copy without size checking (CWE-120). When processing the octet count in TCP syslog messages, the code writes digit characters to a fixed-size heap buffer without properly enforcing bounds during the write operation. Although there is a check for the maximum octet count value, this check occurs after the write operation, allowing the buffer to be overrun by a carefully crafted octet count string.

Attack Vector

The attack vector is network-based, requiring the attacker to send specially crafted TCP syslog messages to an exposed Rsyslog receiver. The attack targets the octet-counted framing mode, which while relatively uncommon, is enabled by default on receivers.

The attacker crafts a syslog message with an excessively long octet count prefix containing only digit characters. When the Rsyslog receiver parses this malformed message, each digit is written to the heap buffer, overflowing its allocated space. The overflow is limited to numeric characters (0-9), which constrains the types of memory values that can be injected.

Exploitation requires direct network access to the Rsyslog TCP reception port. Organizations following the security best practice of not directly exposing syslog receivers to public networks significantly reduce their attack surface.

Detection Methods for CVE-2022-24903

Indicators of Compromise

• Rsyslog service crashes or unexpected restarts with segmentation fault errors in system logs
• Abnormally large or malformed syslog messages in network traffic targeting TCP syslog ports (typically 514/tcp or 6514/tcp)
• Core dump files generated by rsyslogd process indicating heap corruption
• Elevated memory consumption or memory allocation errors in rsyslogd

Detection Strategies

• Monitor Rsyslog service stability and alert on unexpected process terminations or restarts
• Implement network-level inspection for TCP syslog traffic containing unusually long octet count prefixes
• Deploy file integrity monitoring on Rsyslog configuration and binary files
• Review system logs for rsyslogd crash reports and core dump generation events

Monitoring Recommendations

• Enable verbose logging for Rsyslog daemon to capture parsing errors and anomalies
• Configure alerting for rsyslogd service failures through systemd or your init system
• Implement network traffic analysis on syslog reception ports to identify malformed messages
• Monitor for unusual patterns in syslog traffic volume and message structure

How to Mitigate CVE-2022-24903

Immediate Actions Required

• Update Rsyslog to the latest patched version from your distribution's package repository
• Restrict network access to Rsyslog TCP reception modules to trusted internal networks only
• Disable octet-counted framing if not required for your logging infrastructure
• Review and harden firewall rules to limit exposure of syslog services

Patch Information

The Rsyslog maintainers have released a security patch to address this vulnerability. The fix is available in the official Rsyslog repository commit. Distribution-specific patches are available through:

• Debian Security Advisory DSA-5150
• Debian LTS Announcement
• Fedora Package Update
• NetApp Security Advisory

For detailed technical information, refer to the GitHub Security Advisory GHSA-ggw7-xr6h-mmr8.

Workarounds

• Disable octet-counted framing on the imtcp, imptcp, imgssapi, and imhttp modules if not required
• Ensure syslog receivers are not directly exposed to untrusted networks
• Implement network segmentation to isolate logging infrastructure
• Use TLS-enabled syslog reception with client certificate authentication to restrict access

# Disable octet-counted framing in rsyslog configuration
# Add to /etc/rsyslog.conf or /etc/rsyslog.d/security.conf

# For imtcp module - disable octet-counted framing
module(load="imtcp" MaxSessions="500")
input(type="imtcp" port="514" SupportOctetCountedFraming="off")

# For imptcp module - disable octet-counted framing  
module(load="imptcp")
input(type="imptcp" port="514" SupportOctetCountedFraming="off")

# Restart rsyslog after configuration changes
# systemctl restart rsyslog