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Fencer Vulns
medium 5.3

CVE-2026-19879 json

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

published 2026-08-14 2 mo ago modified 2026-11-05 3 d ago also EUVD-2026-58670

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 33%
public exploits
0
none known

Summary

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.

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-19879 updated cvss 5.3

io.undertow/undertow: Undertow: HTTP response header integrity issue due to character truncation

  • Red Hat build of Apache Camel for Spring Boot 4 undertow-core, undertow-parent, undertow-servlet, undertow-websockets-jsr Red Hat Enterprise Linux 8 resteasy, resteasy-javadoc Red Hat Enterprise Linux 9 resteasy, pki-resteasy-core, pki-resteasy-client, pki-resteasy-jackson2-provider, pki-resteasy-servlet-initializer Red Hat Enterprise Linux 10 moditect Red Hat JBoss Enterprise Application Platform 7 undertow-core, undertow-parent, undertow-servlet, undertow-websockets-jsr, jboss-eap-7/eap74-els-openjdk8-openshift-rhel8, jboss-eap-7/eap74-els-openjdk11-openshift-rhel8, +1 more Red Hat JBoss Enterprise Application Platform 8 undertow-core, undertow-servlet, undertow-websockets-jsr
    +2 more products
    Red Hat JBoss Enterprise Application Platform Expansion Pack undertow-core, undertow-servlet, undertow-websockets-jsr Red Hat Single Sign-On 7 undertow-core, undertow-servlet, undertow-websockets-jsr
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2 mo ago

Exploit prediction

0.39% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected products

  • Red Hat Red Hat build of Apache Camel for Spring Boot 4
  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat JBoss Enterprise Application Platform 7
  • Red Hat Red Hat JBoss Enterprise Application Platform 8
  • Red Hat Red Hat JBoss Enterprise Application Platform Expansion Pack
  • Red Hat Red Hat Single Sign-On 7

Classification

Weakness
  • CWE-681 Incorrect Conversion between Numeric Types
Technology feeds

References

Sources

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