CVE-2025-4476 in Red Hat
Summary
by MITRE • 05/16/2025
A denial-of-service vulnerability has been identified in the libsoup HTTP client library. This flaw can be triggered when a libsoup client receives a 401 (Unauthorized) HTTP response containing a specifically crafted domain parameter within the WWW-Authenticate header. Processing this malformed header can lead to a crash of the client application using libsoup. An attacker could exploit this by setting up a malicious HTTP server. If a user's application using the vulnerable libsoup library connects to this malicious server, it could result in a denial-of-service. Successful exploitation requires tricking a user's client application into connecting to the attacker's malicious server.
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Analysis
by VulDB Data Team • 05/06/2026
The vulnerability described in CVE-2025-4476 represents a critical denial-of-service flaw within the libsoup HTTP client library that demonstrates the dangerous impact of improper header parsing in network communication components. This vulnerability specifically targets the processing of HTTP 401 Unauthorized responses, where the WWW-Authenticate header contains a malformed domain parameter that triggers a crash in the client application. The libsoup library, widely used in various applications including web browsers, email clients, and desktop applications, serves as a fundamental HTTP client implementation that handles numerous network interactions, making this vulnerability particularly concerning for widespread exploitation potential. The flaw exists in the library's header parsing mechanism where it fails to properly validate or sanitize the domain parameter within the WWW-Authenticate header, leading to a memory corruption or invalid pointer dereference that results in application termination.
The technical exploitation of this vulnerability requires an attacker to control a malicious HTTP server that responds with a specifically crafted 401 status code containing a malformed domain parameter in the WWW-Authenticate header. This parameter typically consists of improperly formatted or oversized data that causes the libsoup library to attempt memory operations that result in a segmentation fault or similar crash condition. The vulnerability operates at the HTTP protocol level within the client-side library implementation, making it difficult to detect through traditional network monitoring since the malicious behavior occurs during normal HTTP response processing rather than through unusual network traffic patterns. The flaw essentially represents a buffer over-read or improper memory handling issue that falls under CWE-129, which encompasses issues related to improper validation of buffer sizes, and more specifically aligns with CWE-121, concerning buffer overflow conditions in memory management. From an attack framework perspective, this vulnerability maps to the MITRE ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how client-side library vulnerabilities can be leveraged for service disruption.
The operational impact of this vulnerability extends beyond simple application crashes to potentially affect entire user workflows and system availability, particularly in environments where applications rely heavily on automatic authentication and re-authentication mechanisms. When a user's application connects to a malicious server, the client library crashes, forcing the application to terminate or become unresponsive, effectively denying service to the end user. The exploitation requires social engineering or network manipulation to redirect vulnerable applications to the attacker-controlled server, but once successful, the impact is immediate and complete. Applications using affected versions of libsoup may include web browsers, email clients, desktop applications, and mobile applications that implement HTTP authentication, making the potential attack surface quite broad. The vulnerability's impact is particularly severe in enterprise environments where users may automatically connect to various servers during normal operations, increasing the probability of encountering the malicious server. Additionally, since many applications use libsoup as a dependency, a single vulnerable library installation can compromise multiple applications that depend on it, amplifying the potential damage from a single exploitation event.
Mitigation strategies for CVE-2025-4476 should focus on immediate library updates and application patching, as the most effective solution involves upgrading to versions of libsoup that have addressed this specific parsing vulnerability. Organizations should conduct comprehensive inventory assessments to identify all applications and systems that utilize vulnerable versions of libsoup, particularly those that handle HTTP authentication or connect to external servers. Network administrators can implement temporary measures such as blocking connections to known malicious domains or implementing proxy configurations that sanitize HTTP headers before they reach vulnerable applications. Security teams should also consider implementing application whitelisting policies that restrict which applications can make HTTP requests to external servers, reducing the attack surface for exploitation. Additionally, application developers should review their code to ensure proper error handling and validation of HTTP responses, implementing robust input validation for header parameters and implementing proper exception handling to prevent crashes from propagating through the application stack. The vulnerability highlights the importance of proper input validation and secure coding practices in network libraries, emphasizing that even seemingly benign HTTP header parsing can become a critical security issue when insufficiently validated. Organizations should also monitor for similar vulnerabilities in other HTTP client libraries and implement regular security assessments to identify potential weaknesses in their application dependencies.