Executive Summary

This vulnerability exists in libsoup, a GNOME HTTP client/server library used by applications to send network requests. The flaw occurs because libsoup does not properly validate hostnames when setting the HTTP Host header, allowing special characters such as carriage return and line feed (CRLF) to be injected.

An attacker can exploit this by crafting a malicious URI that injects additional HTTP headers or even entire HTTP requests into a single request, a technique known as HTTP request smuggling.

This can lead to Server-Side Request Forgery (SSRF), where the attacker forces the server to make unauthorized requests to internal or external systems.

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Impact Analysis

The vulnerability can cause unexpected HTTP requests, such as POST requests, to be sent in contexts where only safe read operations are expected.

For example, applications like LibreOffice that use libsoup via GIO and GVfs to read remote resources could be tricked into sending attacker-controlled POST requests by opening malicious documents.

This can lead to SSRF attacks, potentially compromising web applications or internal systems, especially on headless servers running document conversion services.

However, the overall impact is considered low because the affected SoupServer component is not widely used in internet infrastructure.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by monitoring HTTP requests for unusual or malformed Host headers containing special characters such as carriage return (\\r) and line feed (\\n) sequences that are normally invalid in hostnames.'}, {'type': 'paragraph', 'content': 'One way to detect exploitation attempts is to capture and inspect HTTP traffic for injected CRLF sequences in the Host header, which may indicate HTTP request smuggling.'}, {'type': 'paragraph', 'content': 'For example, using network packet capture tools like tcpdump or Wireshark, you can filter HTTP traffic and look for suspicious Host headers.'}, {'type': 'list_item', 'content': "tcpdump -A -s 0 'tcp port 80 or tcp port 443' | grep -i 'Host:'"}, {'type': 'list_item', 'content': 'Use Wireshark to filter HTTP requests and inspect Host headers for CRLF or encoded characters such as %0d%0a.'}, {'type': 'paragraph', 'content': 'Additionally, reviewing application logs for unexpected POST requests or unusual HTTP methods triggered by malformed URIs may help identify exploitation attempts.'}] [1]

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Mitigation Strategies

Immediate mitigation steps include validating and sanitizing hostname components before they are used to set HTTP Host headers to ensure they do not contain invalid characters such as CRLF sequences.

Ensure that libsoup or any application using it implements stricter validation on header values to prevent injection of special characters that enable HTTP request smuggling.

If possible, update libsoup to a version where this vulnerability is fixed or apply patches provided by the vendor.

As a temporary measure, monitor and block suspicious HTTP requests with malformed Host headers at the network perimeter or web server level.

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