CVE-2026-26204 Overview
CVE-2026-26204 is a heap-based out-of-bounds write vulnerability affecting Wazuh, a free and open source platform used for threat prevention, detection, and response. The vulnerability exists in the GetAlertData function where an unsigned integer underflow combined with pointer arithmetic wrapping results in writing a NULL byte exactly 1 byte before the start of a buffer allocated by strdup. This heap metadata corruption can be exploited by a malicious actor through a compromised agent to cause denial of service or heap corruption.
Critical Impact
A compromised Wazuh agent can inject specially crafted alerts into the alerts log file monitored by wazuh-logcollector, potentially causing denial of service or heap corruption through heap metadata manipulation.
Affected Products
- Wazuh versions 1.0.0 to 4.14.3
- Wazuh wazuh-logcollector component
- Systems running vulnerable Wazuh server deployments with agent connections
Discovery Timeline
- 2026-04-29 - CVE-2026-26204 published to NVD
- 2026-04-30 - Last updated in NVD database
Technical Details for CVE-2026-26204
Vulnerability Analysis
This vulnerability is classified as CWE-124 (Buffer Underwrite), a memory corruption flaw that occurs when data is written to a memory location before the beginning of an allocated buffer. In the context of the GetAlertData function, the flaw manifests when processing alert data where an unsigned integer underflow causes the write operation to target an invalid memory offset.
The exploitation scenario requires a compromised Wazuh agent that can inject maliciously crafted alert data into the alerts log file. When the wazuh-logcollector processes this crafted input, the integer underflow causes the calculated buffer offset to wrap around, resulting in a write operation at offset -1 from the buffer's starting address. This corrupts heap metadata structures that precede the allocated buffer in memory.
Root Cause
The root cause stems from improper handling of unsigned integer arithmetic in the GetAlertData function. When performing pointer arithmetic with an unsigned integer that has underflowed to a very large value, the resulting memory address wraps around and points to a location before the intended buffer. The function then writes a NULL byte to this invalid location, corrupting adjacent heap metadata. This is a classic buffer underwrite condition where bounds checking fails to account for integer underflow scenarios.
Attack Vector
The attack requires local access with high privileges, specifically through a compromised Wazuh agent. The attack flow proceeds as follows:
- An attacker compromises a Wazuh agent connected to the target Wazuh server
- The attacker crafts a malicious alert payload designed to trigger the integer underflow
- The crafted alert is injected into the alerts log file monitored by wazuh-logcollector
- When wazuh-logcollector processes the malicious alert, the integer underflow occurs in GetAlertData
- A NULL byte is written at offset -1 from the allocated buffer, corrupting heap metadata
- This corruption can lead to denial of service through application crash or potentially further heap exploitation
The vulnerability manifests during alert log processing where specially crafted input triggers an unsigned integer underflow. The subsequent pointer arithmetic causes a write operation to corrupt heap metadata located immediately before the allocated buffer. For detailed technical information, refer to the GitHub Security Advisory GHSA-j4c7-hwjw-8857.
Detection Methods for CVE-2026-26204
Indicators of Compromise
- Unexpected crashes or restarts of the wazuh-logcollector service
- Anomalous or malformed entries in Wazuh alert log files
- Memory-related errors in Wazuh server logs (segmentation faults, heap corruption messages)
- Unusual behavior from connected Wazuh agents attempting to inject large or malformed alerts
Detection Strategies
- Monitor wazuh-logcollector process stability and implement alerting on unexpected service terminations
- Implement log integrity monitoring to detect anomalous or malformed alert entries before processing
- Deploy memory protection mechanisms (ASLR, stack canaries) and monitor for memory corruption events
- Audit connected Wazuh agents for signs of compromise or unauthorized modifications
Monitoring Recommendations
- Configure watchdog monitoring for the wazuh-logcollector service to detect crashes indicative of exploitation attempts
- Implement centralized logging for Wazuh server components with alerting on memory-related errors
- Review and baseline normal alert patterns to identify potentially malicious injected alerts
- Monitor system resource utilization for signs of denial of service conditions
How to Mitigate CVE-2026-26204
Immediate Actions Required
- Upgrade all Wazuh installations to version 4.14.4 or later immediately
- Review connected Wazuh agents for signs of compromise
- Implement network segmentation to limit agent-to-server communication to authorized systems only
- Enable enhanced logging on Wazuh servers to detect potential exploitation attempts
Patch Information
Wazuh has addressed this vulnerability in version 4.14.4. The fix corrects the integer handling in the GetAlertData function to prevent the unsigned integer underflow and subsequent heap metadata corruption. Organizations should upgrade to the patched version as soon as possible.
Patch resources:
Workarounds
- Ensure all connected Wazuh agents are trusted and secure; implement strict agent enrollment policies
- Apply network-level controls to restrict which systems can send data to the wazuh-logcollector
- Deploy application-level monitoring to detect and block anomalous alert data before processing
- Consider implementing additional input validation at the network perimeter for alert log traffic
# Upgrade Wazuh to patched version
# For RPM-based systems:
yum update wazuh-manager -y
# For DEB-based systems:
apt-get update && apt-get install wazuh-manager
# Verify installed version
/var/ossec/bin/wazuh-control info | grep "Wazuh"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
