CVE-2025-31115: XZ Utils Use-After-Free Vulnerability

CVE-2025-31115 Overview

XZ Utils provide a general-purpose data-compression library plus command-line tools. In XZ Utils 5.3.3alpha to 5.8.0, the multithreaded .xz decoder in liblzma has a bug where invalid input can result in a crash. The effects include heap use after free and writing to an address based on the null pointer plus an offset. Applications and libraries using the lzma_stream_decoder_mt function are affected. The bug is fixed in XZ Utils 5.8.1.

Critical Impact
The vulnerability can lead to application crashes and potential data corruption due to memory mismanagement.

Affected Products

XZ Utils 5.3.3alpha
XZ Utils 5.4
XZ Utils 5.8.0

Discovery Timeline

2025-04-03 - CVE-2025-31115 published to NVD
2025-04-07 - Last updated in NVD database

Technical Details for CVE-2025-31115

Vulnerability Analysis

This vulnerability arises from improper handling of inputs in the lzma_stream_decoder_mt function, leading to potential heap use after free conditions. Such a condition could allow attackers to affect the integrity and availability of the affected system.

Root Cause

The root cause of this vulnerability is the lack of adequate validation in handling invalid inputs when decoding with the multithreaded .xz decoder.

Attack Vector

The attack vector for this vulnerability is network-based, requiring remote attackers to send crafted inputs to exploit the flaw.

// Example exploitation code (sanitized)
void exploit_payload() {
    char *payload = "crafted .xz payload";
    lzma_stream_decoder_mt(payload);
}

Detection Methods for CVE-2025-31115

Indicators of Compromise

Unexpected application crashes
Memory access errors
Heap use after free logs

Detection Strategies

Detection can involve monitoring application logs for crashes and validating inputs processed by the xz utilities against expected parameters.

Monitoring Recommendations

Implement monitoring for logs reflecting crashes and integrate telemetry that flags anomalous memory operations within the stream decoding process.

How to Mitigate CVE-2025-31115

Immediate Actions Required

Review and update all instances of XZ Utils
Assess application dependencies on liblzma
Implement additional input validation measures

Patch Information

Upgrade to XZ Utils 5.8.1 or apply the standalone patch available on the Tukaani site.

Workarounds

If upgrading is not immediately possible, restrict access to systems processing .xz files and limit operational inputs accepted by applications depending on the vulnerable function.

bash

# Configuration example
sudo chmod 700 /usr/local/bin/xz