CVE-2012-2098 in Commons-compress
Summary
by MITRE
Algorithmic complexity vulnerability in the sorting algorithms in bzip2 compressing stream (BZip2CompressorOutputStream) in Apache Commons Compress before 1.4.1 allows remote attackers to cause a denial of service (CPU consumption) via a file with many repeating inputs.
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Analysis
by VulDB Data Team • 04/28/2026
The vulnerability identified as CVE-2012-2098 represents a critical algorithmic complexity flaw within the bzip2 compression implementation found in Apache Commons Compress library versions prior to 1.4.1. This issue specifically affects the BZip2CompressorOutputStream class which handles compression operations for bzip2 formatted data streams. The vulnerability stems from the inherent characteristics of the bzip2 algorithm when processing certain types of input data patterns, creating a scenario where computational resources can be exhausted through seemingly benign input files.
The technical flaw manifests when the bzip2 compression algorithm encounters input data containing numerous repeating patterns or sequences. Under normal circumstances, bzip2 compression algorithms are designed to efficiently handle various data types, but the specific implementation in Apache Commons Compress exhibits pathological behavior when processing files with high repetition rates. The algorithm's time complexity degrades significantly from its expected O(n log n) performance to near O(n²) or worse, causing exponential increases in processing time and CPU utilization. This degradation occurs because the compression algorithm's internal sorting mechanisms become increasingly inefficient as the number of repeated elements in the input data grows.
The operational impact of this vulnerability extends beyond simple resource exhaustion, creating substantial security implications for systems that process untrusted bzip2 compressed data. Remote attackers can exploit this weakness by crafting specially designed files containing many repeating inputs, which when processed through the vulnerable Apache Commons Compress library cause significant CPU consumption. This allows for effective denial of service attacks where legitimate system resources are consumed at an unsustainable rate, potentially leading to system instability, application crashes, or complete service unavailability. The vulnerability is particularly dangerous in environments where automated decompression occurs, such as web applications, file processing systems, or any service that accepts and processes compressed data from untrusted sources.
Systems utilizing Apache Commons Compress library versions prior to 1.4.1 are at risk of exploitation by attackers who can submit maliciously crafted bzip2 files to trigger the algorithmic complexity issue. The vulnerability aligns with CWE-400, which categorizes "Uncontrolled Resource Consumption" as a critical weakness, and demonstrates characteristics consistent with the ATT&CK technique T1499.004, "Network Denial of Service," where attackers consume network resources to disrupt service availability. Organizations should immediately upgrade to Apache Commons Compress version 1.4.1 or later, which includes patches addressing the algorithmic complexity issues in the bzip2 compression implementation. Additional mitigations include implementing input validation controls, limiting file size restrictions for compressed data, and deploying rate limiting mechanisms to prevent excessive resource consumption during decompression operations. The vulnerability highlights the importance of understanding algorithmic complexity characteristics in cryptographic and compression libraries, particularly when processing untrusted inputs in security-sensitive applications.