Executive Summary

This vulnerability in FreshRSS versions 1.27.0 to before 1.28.0 allows an attacker to cause a global denial of access to feeds by modifying proxy responses to return a 429 Retry-After status for a large list of feeds on the instance, making the service unusable for most users. It has been fixed in version 1.28.0.

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Impact Analysis

The vulnerability can impact you by making the FreshRSS service unusable for the majority of users due to a global denial of access to feeds, which disrupts normal access and availability of RSS feeds.

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Mitigation Strategies

Upgrade FreshRSS to version 1.28.0 or later, as this version contains the patch that fixes the vulnerability allowing attackers to cause a denial of service by modifying responses to 429 Retry-After status codes.

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Compliance Impact

The vulnerability impacts availability by allowing denial of service to RSS feeds but does not affect confidentiality or integrity of data. There is no information indicating that this vulnerability directly affects compliance with common standards and regulations such as GDPR or HIPAA. [1, 3]

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Detection Guidance

This vulnerability can be detected by monitoring HTTP responses from FreshRSS feed requests for unusual 429 Too Many Requests status codes accompanied by Retry-After headers with large values (e.g., Retry-After: 10000). To detect exploitation attempts or presence of malicious proxies, you can capture and inspect HTTP traffic to identify repeated 429 responses with Retry-After headers affecting multiple feeds. Commands such as using curl to fetch feeds and observe headers, or using network traffic analysis tools like tcpdump or Wireshark to filter HTTP/2 429 responses, can help. For example, you can run: 1) curl -I <feed_url> to check HTTP headers for 429 status and Retry-After header; 2) tcpdump -i <interface> -A 'tcp port 80 or 443' | grep -i 'HTTP/2 429' to capture relevant HTTP responses; 3) Use proxy tools like Burp Suite to intercept and analyze feed responses for manipulated Retry-After headers. These methods help identify if a proxy is injecting false Retry-After headers causing denial of service. [1]

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