The vulnerability lies in Undertow’s response header construction path where the writeString() method silently casts 16‑bit Unicode characters to 8‑bit bytes. This truncates unsupported Unicode characters into ASCII control characters or symbols. When an attacker supplies crafted Unicode input that an application places into response headers, the resulting header values can be corrupted, potentially exposing information or altering request handling if the application fails to sanitize the data.

The flaw affects Red Hat Enterprise Linux 8, 9 and 10, Red Hat JBoss Enterprise Application Platform 7 and 8 with the Expansion Pack, Red Hat Single Sign‑On 7, and Red Hat build of Apache Camel for Spring Boot 4. The specific affected product releases are not enumerated in the available data.

The CVSS score of 5.3 indicates a moderate severity, and the EPSS score is not available, suggesting no quantified evidence of current exploitation. The vulnerability is not listed in the CISA KEV catalog. An attacker can exploit it remotely by crafting HTTP requests that embed Unicode characters in user‑controlled fields that are subsequently reflected in HTTP response headers. The narrow cast causes these characters to be truncated into ASCII control characters or symbols, which can lead to integrity violations or limited information disclosure if the application does not perform proper input validation. The attack requires only the ability to send HTTP requests to the affected server and does not rely on elevated privileges.