CVE-2026-19879

Io.undertow/undertow: undertow: http response header integrity issue due to character truncation

Published Aug 14, 2026 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Workaround

Applications utilizing Undertow should implement robust input validation and sanitization for all user-controlled data before it is placed into HTTP response headers. It is recommended to restrict header values to printable ASCII characters (0x20–0x7E) at the application level. Where available, use framework-provided header-safe encoding mechanisms to ensure proper handling of special characters.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
cpe:/a:redhat:enterprise_linux:10
cpe:/a:redhat:enterprise_linux:8
cpe:/a:redhat:enterprise_linux:9
Type Values Removed Values Added
First Time appeared Redhat build Of Apache Camel For Spring Boot
Redhat jboss Enterprise Application Platform Expansion Pack
Redhat single Sign On
Redhat undertow
Vendors & Products Redhat build Of Apache Camel For Spring Boot
Redhat jboss Enterprise Application Platform Expansion Pack
Redhat single Sign On
Redhat undertow
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title Io.undertow/undertow: undertow: http response header integrity issue due to character truncation
First Time appeared Redhat
Redhat camel Spring Boot
Redhat enterprise Linux
Redhat jboss Enterprise Application Platform
Redhat jbosseapxp
Redhat red Hat Single Sign On
Weaknesses CWE-681
CPEs cpe:/a:redhat:camel_spring_boot:4
cpe:/a:redhat:jboss_enterprise_application_platform:7
cpe:/a:redhat:jboss_enterprise_application_platform:8
cpe:/a:redhat:jbosseapxp
cpe:/a:redhat:red_hat_single_sign_on:7
cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat camel Spring Boot
Redhat enterprise Linux
Redhat jboss Enterprise Application Platform
Redhat jbosseapxp
Redhat red Hat Single Sign On
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N'}