CVE-2025-66485 is a vulnerability identified in IBM Aspera Shares versions 1.9.9 through 1.11.0, categorized under CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax. The root cause is insufficient validation and sanitization of the HTTP Host header input, which enables an attacker to inject malicious content into HTTP response headers. This injection can be exploited to conduct various attacks such as cross-site scripting (XSS), where malicious scripts execute in the context of the victim's browser; cache poisoning, which manipulates cached content to serve malicious payloads to users; and session hijacking, allowing attackers to steal or manipulate user sessions. The vulnerability requires network access and low privileges (PR:L), does not require user interaction (UI:N), and affects confidentiality and integrity but not availability. The scope is unchanged, meaning the vulnerability affects only the vulnerable component without extending to other components. Although no public exploits are currently known, the flaw's nature makes it a candidate for targeted attacks against organizations using IBM Aspera Shares for secure file transfer and collaboration. The vulnerability was published in April 2026, with a CVSS v3.1 base score of 5.4, reflecting a medium severity level.

The vulnerability can lead to unauthorized disclosure of sensitive information through session hijacking and cross-site scripting attacks, compromising user credentials and data confidentiality. Cache poisoning can degrade trust in the affected service by delivering malicious or altered content to users. These impacts can disrupt secure file sharing workflows, potentially exposing intellectual property or sensitive organizational data. Organizations relying on IBM Aspera Shares for critical file transfer operations may face reputational damage, regulatory compliance issues, and operational disruptions if exploited. Since exploitation does not require user interaction but does require low privileges, insider threats or attackers with limited access could leverage this vulnerability to escalate their impact. The absence of availability impact means service disruption is unlikely, but confidentiality and integrity risks remain significant.

Organizations should immediately assess their deployment of IBM Aspera Shares and identify affected versions (1.9.9 through 1.11.0). Since no official patches are currently linked, administrators should implement strict input validation and sanitization of HTTP Host headers at the web server or application gateway level to block malicious header injection attempts. Employing Web Application Firewalls (WAFs) with custom rules to detect and block anomalous Host header values can provide an effective interim defense. Monitoring logs for unusual Host header patterns and conducting regular security assessments can help detect exploitation attempts early. Additionally, restricting access to the Aspera Shares interface to trusted networks and enforcing least privilege principles reduces exposure. Organizations should stay alert for IBM's official patches or updates and apply them promptly once available. Educating users about phishing and session hijacking risks complements technical controls.