CVE-2026-21850 in AION
Summary
by MITRE • 11/06/2026
HCL AION is affected by a vulnerability where user-controlled input could be included in HTTP response headers without proper neutralization of CR/LF characters. This may allow an attacker to inject headers or split responses, potentially resulting in unintended behavior or security impact under certain conditions.
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Analysis
by VulDB Data Team • 11/06/2026
The identified vulnerability in HCL AION represents a classic instance of HTTP Response Splitting, a flaw rooted in the improper handling of user-supplied input within server-side response generation logic. This specific weakness occurs when an application incorporates data provided by users directly into HTTP headers without adequately sanitizing or validating that input for control characters such as carriage returns and line feeds. In standard web architecture, HTTP responses are structured with distinct header sections followed by a blank line to separate them from the message body. If an attacker can inject these specific newline characters into a field destined for the response headers, they effectively terminate the current header block prematurely. This allows subsequent content injected by the attacker to be interpreted as new HTTP headers or even the start of the response body, fundamentally breaking the expected structure of the communication between the server and the client.
From a technical perspective, this vulnerability aligns with CWE-113, which describes Improper Neutralization of CRLF Sequences in HTTP Headers, often referred to as HTTP Response Splitting. The core issue lies in the lack of strict input validation or encoding mechanisms that would prevent special characters from being interpreted literally by downstream parsers such as web browsers, proxies, or firewalls. When an attacker successfully injects a carriage return followed by a line feed into a header value, they can manipulate how intermediate devices process the response. For instance, if the vulnerability affects headers like Set-Cookie, Location, or Content-Type, the impact can be severe because these fields dictate critical aspects of client behavior and session management. The absence of proper neutralization means that the application trusts user input implicitly during header construction, creating a direct pathway for injection attacks without requiring authentication in many scenarios depending on where the vulnerable parameter is located within the application flow.
The operational impact of this vulnerability extends beyond simple data manipulation to include significant security risks such as Cross-Site Scripting and session hijacking. By splitting the response, an attacker can inject arbitrary HTTP headers that instruct a web browser to execute malicious scripts stored in cookies or other injected fields. This technique is often used to bypass Content Security Policy restrictions because the injected script may be interpreted as part of a trusted domain's response rather than external content. Furthermore, if the vulnerability allows for cache poisoning, an attacker could manipulate shared caches like CDNs or reverse proxies to serve malicious payloads to multiple users who request the same resource. This amplifies the scope of the attack from targeting individual sessions to potentially compromising entire user bases through cached responses that contain injected headers containing JavaScript code or other harmful directives.
Mitigation strategies must focus on rigorous input validation and output encoding at both the application layer and infrastructure level. Developers should implement strict allow-listing for all inputs used in HTTP header construction, ensuring that only expected alphanumeric characters and safe punctuation are permitted. Any control characters such as CR and LF must be explicitly rejected or encoded before being processed by the web server framework. Additionally, utilizing modern web frameworks that automatically handle CRLF escaping can significantly reduce the risk of this vulnerability occurring due to developer error. On the infrastructure side, configuring reverse proxies like Nginx or Apache with strict header validation rules can provide a secondary layer of defense by stripping or rejecting malformed headers before they reach end users. Regular security testing using dynamic application security scanning tools that specifically target HTTP response splitting patterns is also recommended to identify and remediate such flaws proactively within the software development lifecycle.