CVE-2026-19879 Io.undertow/undertow: undertow: http response header integrity issue due to character truncation
Remote attackers can exploit Unicode truncation in Undertow HTTP headers to cause integrity issues or information disclosure via unsanitized input.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-19879?
CVE-2026-19879 is a medium-severity vulnerability in Red Hat Enterprise Linux 10, published on 14 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-681
Which versions are affected by CVE-2026-19879?
How do I fix CVE-2026-19879?
No fix has been published for CVE-2026-19879 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-19879 being exploited?
There is no known exploitation of CVE-2026-19879 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-19879, GHSA-2crv-pxj9-66x8, UBUNTU-CVE-2026-19879.