CVE-2025-0825 is a medium severity vulnerability classified under CWE-113, which pertains to improper neutralization of CRLF (Carriage Return Line Feed) sequences in HTTP headers, commonly known as HTTP Request/Response Splitting. This vulnerability affects cpp-httplib versions from v0.17.3 through v0.18.3. The root cause is the failure of the library to properly filter CRLF characters when they are prefixed with a null byte (\0). This bypass allows an attacker to inject CRLF sequences into HTTP headers, which can lead to HTTP Response Splitting attacks. Such attacks enable an adversary to manipulate the HTTP response headers and body, potentially causing multiple malicious effects including Cross-Site Scripting (XSS), cache poisoning, session fixation, and web cache deception. The vulnerability is exploitable remotely without authentication (AV:N/AC:L/PR:N), but requires user interaction (UI:A), and impacts the integrity of the HTTP response (VI:H). The CVSS 4.0 score is 6.9, indicating a medium severity level. No known exploits are currently reported in the wild, and no official patches have been linked yet. The vulnerability was reserved and published in early 2025, highlighting its recent discovery. Given that cpp-httplib is a lightweight C++ HTTP library used in embedded systems, IoT devices, and some web services, the affected systems may include custom applications and services relying on this library for HTTP communications. Attackers exploiting this vulnerability could manipulate HTTP headers to inject malicious payloads, leading to client-side attacks or disruption of web services.

For European organizations, the impact of CVE-2025-0825 can be significant depending on the extent of cpp-httplib usage within their infrastructure. Organizations utilizing custom-built applications, embedded devices, or IoT solutions that incorporate vulnerable versions of cpp-httplib may face risks of HTTP response manipulation. This can lead to XSS attacks, which compromise user confidentiality and integrity by executing malicious scripts in users' browsers, potentially stealing credentials or session tokens. Additionally, HTTP response splitting can disrupt service availability by poisoning caches or causing unexpected behavior in web applications. Sectors such as finance, healthcare, and critical infrastructure in Europe, which often deploy embedded or custom HTTP services, could be particularly vulnerable. The medium severity rating suggests that while the vulnerability is not trivially exploitable without user interaction, the consequences of successful exploitation can be impactful, especially in environments where sensitive data is transmitted or where web application integrity is paramount. Furthermore, the lack of patches at the time of publication means organizations must proactively assess and mitigate risks to prevent exploitation.

European organizations should undertake the following specific mitigation steps: 1) Inventory and identify all applications and devices using cpp-httplib versions v0.17.3 through v0.18.3, focusing on embedded systems and custom HTTP services. 2) Apply patches or updates as soon as they become available from the cpp-httplib maintainers; if no official patch exists, consider upgrading to a version confirmed to sanitize CRLF sequences properly. 3) Implement input validation and sanitization at the application layer to detect and neutralize CRLF injection attempts, especially those involving null byte prefixes. 4) Employ Web Application Firewalls (WAFs) with rules designed to detect and block HTTP header injection and response splitting patterns. 5) Monitor HTTP traffic for anomalies indicative of response splitting or header manipulation attacks. 6) Educate developers and security teams about the risks of improper header handling and encourage secure coding practices to prevent similar vulnerabilities. 7) Where feasible, isolate vulnerable services behind reverse proxies that can sanitize HTTP headers before forwarding requests or responses. These targeted actions go beyond generic advice by focusing on the specific nature of the vulnerability and the characteristics of the affected library.