CVE-2025-27821: Apache Patches Out-of-Bounds Write Flaw in Hadoop HDFS Client

The Apache Software Foundation has released a security update for Apache Hadoop, the backbone of big data processing for enterprises worldwide. A new vulnerability, tracked as CVE-2025-27821, has been discovered in the HDFS native client, exposing systems to potential crashes or data corruption due to memory mismanagement.

The flaw affects the URI parser within the native client, a critical component responsible for interpreting addresses and locating data across distributed file systems.

The vulnerability is classified as an “Out-of-bounds Write,” a memory safety error where software writes data past the end of the intended buffer. In this case, the issue resides specifically in how the native HDFS client parses Uniform Resource Identifiers (URIs).

According to the security bulletin, the flaw allows for an “Out-of-bounds Write vulnerability in Apache Hadoop HDFS native client”. While the severity is rated as “Moderate,” memory safety vulnerabilities are often precursors to stability issues (denial of service) or, in more complex scenarios, unexpected code execution.

Because Hadoop is designed to “scale up from single servers to thousands of machines,” stability at the application layer is paramount. A flaw in the client side could disrupt the reliable, distributed processing that organizations depend on.

The vulnerability impacts a specific range of the software. Administrators should check their deployments for HDFS native client (org.apache.hadoop:hadoop-hdfs-native-client) versions:

• From 3.2.0
• Before 3.4.2

The Apache team has moved to close this gap with the release of version 3.4.2.

Users running affected versions of the HDFS native client are recommended to upgrade to version 3.4.2, which fixes the issue ensuring their data lakes remain watertight against this specific memory flaw.

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