Snappier SnappyStream Decompression Infinite Loop Vulnerability

The Snappier library, specifically the SnappyStream class, is susceptible to a denial-of-service vulnerability when decompressing malformed Snappy streams in framed format. An attacker who can control the input to the SnappyStream decompression process can trigger an infinite loop, leading to excessive CPU consumption and thread exhaustion. This issue affects applications using Snappier version 1.3.0 and earlier. The vulnerability stems from an unhandled condition in the decompression logic, causing the SnappyStreamDecompressor.Decompress method to repeatedly call Crc32CAlgorithm.Append without termination. Standard exception handling mechanisms (try/catch blocks) are ineffective in preventing the hang, making it difficult to mitigate without terminating the affected process.

Attack Chain

1. An attacker crafts a malformed Snappy compressed data stream (as small as 15 bytes).
2. The attacker sends this malformed stream to a service or application using the Snappier library for decompression.
3. The application instantiates a SnappyStream object with CompressionMode.Decompress to handle the incoming data stream.
4. The application calls CopyTo() or a similar method on the SnappyStream to decompress the data.
5. The SnappyStreamDecompressor.Decompress method is invoked internally.
6. Due to the malformed input, an infinite loop occurs within SnappyStreamDecompressor.Decompress involving repeated calls to Crc32CAlgorithm.Append.
7. A single CPU core is consumed at 100% by the affected thread.
8. The application hangs indefinitely, requiring termination to recover.

Impact

Successful exploitation of this vulnerability results in a denial-of-service condition. An attacker can remotely trigger the infinite loop by sending malicious data to any application that utilizes the vulnerable Snappier.SnappyStream for decompression. This can lead to resource exhaustion, application unavailability, and potentially impact other services relying on the same system. Since the try/catch doesn’t work, the service will remain inoperable until manually restarted.

Recommendation

• Upgrade to a patched version of the Snappier library that addresses CVE-2026-44302.
• Implement input validation and sanitization on data streams prior to decompression using Snappier.SnappyStream.
• Monitor CPU usage for processes utilizing the Snappier library. Deploy the process monitoring rule below to detect potential exploitation attempts based on high CPU usage.