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The vulnerability CVE-2025-XXXXX in Bugsink stems from an improper handling of Brotli-compressed HTTP request bodies. An attacker can send a specially crafted ‘Brotli bomb’—a small, highly compressed payload that decompresses to an extremely large data stream, often gigabytes of repetitive data like zeros. The flaw exists because the server’s Brotli decompressor allocates memory for the entire decompressed data stream before applying any configured size limits or validation checks. This happens during the initial request processing phase, which does not require user authentication. By repeatedly sending these malicious payloads to a known Data Source Name (DSN) endpoint, an attacker can exhaust the server’s available memory, leading to a complete denial of service for legitimate users.
Platform: Bugsink
Version: < 2.0.5
Vulnerability: Brotli Bomb DoS
Severity: High
date: 2025-11-08
Prediction: Patch 2025-11-20
What Undercode Say:
Crafting a Brotli bomb using Python echo 'x' 1000000000 | python3 -c "import brotli; import sys; sys.stdout.buffer.write(brotli.compress(sys.stdin.buffer.read()))" > bomb.br Sending the bomb with curl to a target DSN curl -X POST -H "Content-Encoding: br" --data-binary @bomb.br http://target.com/api/dsn
// Pseudo-code showing excessive memory allocation size_t decompressed_size = BrotliDecompressedSize(compressed_data); char output_buffer = malloc(decompressed_size); // Massive allocation triggered by bomb BrotliDecompress(compressed_data, compressed_size, output_buffer);
How Exploit:
1. Attacker identifies the target’s DSN endpoint.
- Crafts a small Brotli bomb payload that decompresses to gigabytes of data.
- Sends the payload in an HTTP POST request with `Content-Encoding: br` header.
- Server decompresses the payload, consuming all available RAM.
5. Service becomes unresponsive, causing a Denial-of-Service.
Protection from this CVE
Upgrade to Bugsink version 2.0.5 or later.
Implement ingress filtering to limit HTTP request body sizes before decompression.
Use a WAF to detect and block Brotli bomb patterns.
Configure reverse proxies to validate Content-Encoding headers.
Impact:
Remote Unauthenticated Denial-of-Service.
Complete server resource exhaustion (RAM).
Service unavailability for all users.
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Sources:
Reported By: github.com
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