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  4. CVE 2026 19879 ioundertowundertow undertow http response header
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Back to active CVEs
Medium · CVSS 5.3CVE-2026-19879

Io.undertow/undertow: undertow: http response header integrity issue due to character truncationCVE-2026-19879

Answer in brief

CVE-2026-19879 records a Medium severity (CVSS 5.3) vulnerability in Io.undertow/undertow: undertow: http response header integrity issue due to character truncation. The current sources do not mark it as known exploited. The current feed maps Red Hat/jboss-eap-7/eap74-els-openjdk11-openshift-rhel8 (generic), Red Hat/jboss-eap-7/eap74-els-openjdk17-openshift-rhel8 (generic), Red Hat/jboss-eap-7/eap74-els-openjdk8-openshift-rhel8 (generic), Red Hat/moditect (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 14, 2026Updated Nov 5, 2026Source checked Nov 13, 2026First seen by HOL Aug 14, 2026Material review Nov 5, 2026
Upstream Advisory

Key facts

Risk
Medium · CVSS 5.3
Exploitation
Not marked as known exploited
Affected software
11 mapped packages or products
Fix availability
Not reported

Why this deserves its current priority

CVSS is 5.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Red Hat/jboss-eap-7/eap74-els-openjdk11-openshift-rhel8 (generic), Red Hat/jboss-eap-7/eap74-els-openjdk17-openshift-rhel8 (generic), Red Hat/jboss-eap-7/eap74-els-openjdk8-openshift-rhel8 (generic), Red Hat/moditect (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
Red Hat/jboss-eap-7/eap74-els-openjdk11-openshift-rhel8generic*Not reported
Red Hat/jboss-eap-7/eap74-els-openjdk17-openshift-rhel8generic*Not reported
Red Hat/jboss-eap-7/eap74-els-openjdk8-openshift-rhel8generic*Not reported
Red Hat/moditectgeneric*Not reported
Red Hat/pki-core:10.6/resteasygeneric*Not reported
Red Hat/pki-deps:10.6/resteasygeneric*Not reported
Red Hat/resteasygeneric*Not reported
Red Hat/undertow-coregeneric*Not reported
Red Hat/undertow-parentgeneric*Not reported
Red Hat/undertow-servletgeneric*Not reported
Red Hat/undertow-websockets-jsrgeneric*Not reported

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for Red Hat/jboss-eap-7/eap74-els-openjdk11-openshift-rhel8, Red Hat/jboss-eap-7/eap74-els-openjdk17-openshift-rhel8, Red Hat/jboss-eap-7/eap74-els-openjdk8-openshift-rhel8.
  2. 2Review the reported fix. Source-reported 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.

Evidence timeline and material changes

  1. Published upstream

    Aug 14, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Nov 5, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Aug 14, 2026

Sources and claim methodology

  • Source referenceaccess.redhat.com
  • Source referencebugzilla.redhat.com
Upstream source 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.

Quoted source text, attributed separately from HOL analysis.

Record context

Vulnerability class
Vulnerability
EPSS
Not reported
CWE IDs
CWE-681
Source
CVE List V5
Source checked
Nov 13, 2026
References
2 linked sources
Open source record