CVE-2026-19879 — Io.undertow/undertow: undertow: http response header integrity issue due to character truncation
A flaw was found in Undertow, an HTTP server, within its HTTP response header writing path. The `writeString()` method performs a silent narrowing cast from 16-bit Unicode chara…
Published: 2026-08-14 · CVSS: 5.3 · CVSS 3.1
A flaw was found in Undertow, an HTTP server, within its HTTP response header writing path. The `writeString()` method performs a silent narrowing cast from 16-bit Unicode characters to 8-bit bytes when writing HTTP response header values. A remote attacker can exploit this by supplying specific Unicode characters in user-controlled input that an application places into response headers. This can lead to the truncation of these characters into ASCII control characters or special symbols, potentially resulting in limited integrity impact or information disclosure if the application does not properly sanitize user input.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7