CVE-2025-27821: Apache Hadoop Buffer Overflow Vulnerability

CVE-2025-27821 Overview

CVE-2025-27821 is an Out-of-bounds Write vulnerability affecting the Apache Hadoop HDFS native client. This memory corruption vulnerability exists in Apache Hadoop versions 3.2.0 through 3.4.1, allowing attackers to potentially write data beyond allocated memory boundaries in the HDFS native client component.

Out-of-bounds write vulnerabilities (CWE-787) occur when software writes data past the end of an allocated buffer, which can lead to memory corruption, application crashes, or potentially arbitrary code execution. In the context of Apache Hadoop's distributed file system, this vulnerability could impact data integrity and system stability across Hadoop clusters.

Critical Impact

This vulnerability enables network-based attacks against Apache Hadoop HDFS native clients without requiring authentication, potentially compromising confidentiality, integrity, and availability of Hadoop cluster data.

Affected Products

• Apache Hadoop versions 3.2.0 through 3.4.1
• Apache Hadoop HDFS native client component
• Organizations running Hadoop clusters with affected versions

Discovery Timeline

• January 26, 2026 - CVE-2025-27821 published to NVD
• January 27, 2026 - Last updated in NVD database

Technical Details for CVE-2025-27821

Vulnerability Analysis

The vulnerability resides within the HDFS native client component of Apache Hadoop. The native client provides high-performance file system operations through native code implementations, which can be susceptible to memory safety issues that managed code would typically prevent.

An out-of-bounds write vulnerability in this component allows an attacker to corrupt memory by writing data beyond the boundaries of allocated buffers. The network-accessible nature of this vulnerability means attackers can potentially exploit it remotely without requiring user interaction or prior authentication.

The impact spans across confidentiality, integrity, and availability, as successful exploitation could allow attackers to read sensitive data, modify system behavior, or cause service disruptions in Hadoop environments.

Root Cause

The root cause of CVE-2025-27821 is improper boundary checking in the HDFS native client code. When processing certain inputs, the native client fails to properly validate buffer sizes before performing write operations, allowing data to be written past the allocated memory region. This is a classic CWE-787 (Out-of-bounds Write) vulnerability pattern that occurs when software does not properly validate the size of input data against the size of allocated buffers.

Attack Vector

The vulnerability can be exploited over the network, making it accessible to remote attackers. The attack does not require prior privileges or user interaction, lowering the barrier for exploitation. An attacker could craft malicious requests to the HDFS native client that trigger the out-of-bounds write condition.

The exploitation involves sending specially crafted data to a Hadoop cluster running vulnerable versions of the HDFS native client. When the client processes this malicious input without proper bounds checking, it writes data beyond the intended buffer, potentially overwriting adjacent memory regions.

For detailed technical information about this vulnerability, refer to the Apache Security Mailing List Thread and the OpenWall OSS Security Discussion.

Detection Methods for CVE-2025-27821

Indicators of Compromise

• Unexpected crashes or segmentation faults in HDFS native client processes
• Memory corruption errors or abnormal memory usage patterns in Hadoop DataNode or NameNode logs
• Unusual network traffic patterns to HDFS client ports
• Core dumps indicating memory boundary violations in Hadoop native libraries

Detection Strategies

• Monitor Hadoop cluster logs for native client crashes, memory errors, or segmentation faults
• Implement network intrusion detection rules to identify malformed HDFS protocol requests
• Use memory debugging tools (Valgrind, AddressSanitizer) in development environments to detect buffer overflow conditions
• Deploy endpoint detection solutions like SentinelOne to identify exploitation attempts

Monitoring Recommendations

• Enable verbose logging on HDFS native client operations during the vulnerability remediation period
• Set up alerting for abnormal process terminations in Hadoop services
• Monitor system memory utilization and crash reports across all nodes in the Hadoop cluster
• Implement network traffic analysis to detect anomalous HDFS protocol communications

How to Mitigate CVE-2025-27821

Immediate Actions Required

• Upgrade Apache Hadoop to version 3.4.2 or later, which contains the fix for this vulnerability
• Audit all Hadoop clusters to identify instances running affected versions (3.2.0 through 3.4.1)
• Implement network segmentation to limit access to HDFS native client interfaces
• Review access controls and ensure only authorized systems can communicate with Hadoop services

Patch Information

Apache has released version 3.4.2 which addresses this out-of-bounds write vulnerability. Organizations running Apache Hadoop versions 3.2.0 through 3.4.1 should prioritize upgrading to the patched version. The security advisory is available on the Apache Security Mailing List.

Workarounds

• If immediate patching is not possible, consider disabling the native client and using the Java-based HDFS client instead
• Restrict network access to HDFS services using firewall rules to limit exposure to trusted networks only
• Implement application-level firewalls or proxies that can filter malformed HDFS requests
• Monitor and audit all traffic to HDFS endpoints until patching is complete

# Configuration example - Restrict HDFS access via iptables
# Allow only trusted networks to access HDFS ports
iptables -A INPUT -p tcp --dport 8020 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 8020 -j DROP
iptables -A INPUT -p tcp --dport 9000 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 9000 -j DROP