CVE-2025-4476 is a denial-of-service vulnerability identified in the libsoup HTTP client library, which is commonly used in Linux environments including Red Hat Enterprise Linux 10. The vulnerability arises when a libsoup client receives an HTTP 401 Unauthorized response containing a specially crafted domain parameter within the WWW-Authenticate header. This malformed header triggers a NULL pointer dereference within the libsoup client code, causing the client application to crash. The root cause is improper handling of the domain parameter in the authentication header, leading to dereferencing a null pointer without adequate validation. An attacker can exploit this by setting up a malicious HTTP server that sends the crafted 401 response. When a vulnerable client application connects to this server, the crash results in a denial-of-service condition, impacting the availability of the client application. Exploitation does not require privileges or authentication but does require user interaction to connect to the malicious server, such as visiting a malicious URL or being redirected. The vulnerability has a CVSS 3.1 base score of 4.3, reflecting medium severity due to its limited impact on confidentiality and integrity and the requirement for user interaction. No known exploits have been reported in the wild as of the publication date. The vulnerability affects Red Hat Enterprise Linux 10 and potentially other distributions or applications using the vulnerable libsoup version. The lack of patch links suggests that fixes may be pending or recently released. This vulnerability is primarily a threat to availability, potentially disrupting client applications relying on libsoup for HTTP communications.

For European organizations, this vulnerability poses a risk primarily to the availability of client applications using libsoup on Red Hat Enterprise Linux 10. Organizations with automated or user-initiated HTTP client connections to external servers could experience application crashes if users connect to malicious or compromised servers that exploit this flaw. This could disrupt business operations, especially in sectors relying on continuous client-server communications such as finance, telecommunications, and critical infrastructure. Although the impact on confidentiality and integrity is negligible, denial-of-service conditions can lead to downtime, loss of productivity, and potential cascading effects if critical client applications are affected. The requirement for user interaction limits mass exploitation but targeted phishing or redirection attacks could be used to trigger the vulnerability. European organizations with strict uptime requirements and those operating in regulated industries may face compliance and operational risks if this vulnerability is exploited.

To mitigate CVE-2025-4476, European organizations should prioritize the following actions: 1) Monitor Red Hat and libsoup project advisories closely and apply security patches promptly once available to eliminate the vulnerability. 2) Implement network controls to restrict client application connections to trusted and verified HTTP servers, reducing exposure to malicious servers. 3) Employ web filtering and DNS filtering solutions to block access to known malicious domains and prevent redirection to attacker-controlled servers. 4) Educate users about the risks of connecting to untrusted URLs or servers, emphasizing caution with links received via email or other communication channels. 5) Where feasible, configure client applications to validate or sanitize HTTP authentication headers or use alternative HTTP client libraries not affected by this vulnerability. 6) Monitor application logs and network traffic for unusual 401 Unauthorized responses with malformed headers that could indicate exploitation attempts. 7) Consider deploying runtime application self-protection (RASP) or endpoint detection and response (EDR) tools capable of detecting and mitigating application crashes caused by malformed network inputs. These measures, combined with patching, will reduce the risk and impact of exploitation.