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How the CVE Works:
This vulnerability exploits the Brotli decompression algorithm within Bugsink’s envelope processing. An unauthenticated attacker can send a specially crafted, malicious Brotli-compressed input to a known Bugsink DSN endpoint. This crafted input is designed to trigger a pathological worst-case scenario during the decompression routine, causing the process to enter an extremely long or near-infinite loop. Consequently, the affected Bugsink instance consumes 100% of a CPU core, rendering it unresponsive to legitimate requests and achieving a denial-of-service state. The attack is feasible without credentials in common deployments where the DSN is exposed, such as in client-side JavaScript or mobile application configurations.
Platform: Bugsink
Version: < 2.0.6
Vulnerability: CPU Exhaustion
Severity: High
date: 2025-11-08
Prediction: Patch ETA: 2025-11-15
What Undercode Say:
Simulating a request with a malicious Brotli payload curl -X POST https://your-dsn.ingest.bugsink.com/api/event/ \ -H 'Content-Encoding: br' \ --data-binary @malicious_payload.br
Concept code for generating a problematic Brotli stream import brotli Crafting input that creates excessive backreferences crafted_data = b'\x00' 1000000 Simplified example compressed_payload = brotli.compress(crafted_data, quality=11) Send compressed_payload to target
How Exploit:
1. Identify the target’s Bugsink DSN.
- Craft a malicious Brotli payload designed for maximum CPU consumption during decompression.
- Send the payload in an HTTP POST request to the `/api/event/` endpoint with the `Content-Encoding: br` header.
- Observe the target service becoming unresponsive due to CPU exhaustion.
Protection from this CVE:
Upgrade Bugsink to version 2.0.6 or later immediately. If an immediate upgrade is not possible, implement network-level controls to restrict access to the ingestion endpoint from untrusted sources or use a Web Application Firewall (WAF) capable of inspecting and filtering Brotli-encoded content for anomalous patterns.
Impact:
Successful exploitation leads to a complete denial of service, rendering the Bugsink event processing service unavailable. This can halt error reporting and monitoring for dependent applications, potentially obscuring other operational issues from view and impacting application observability.
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Sources:
Reported By: github.com
Extra Source Hub:
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