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.
Published: 2026-08-14
Score: 5.3 Medium
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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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

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History

Fri, 14 Aug 2026 18:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

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

Fri, 14 Aug 2026 15:00:00 +0000

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'}

Subscriptions

Redhat Camel Spring Boot Enterprise Linux Jboss Enterprise Application Platform Jbosseapxp Red Hat Single Sign On
cve-icon MITRE

Status: PUBLISHED

Assigner: redhat

Published:

Updated: 2026-08-14T18:06:23.158Z

Reserved: 2026-08-14T14:26:12.605Z

Link: CVE-2026-19879

cve-icon Vulnrichment

Updated: 2026-08-14T17:41:35.726Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-08-14T15:17:09.310

Modified: 2026-08-14T19:07:46.080

Link: CVE-2026-19879

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-14T16:30:05Z

Weaknesses