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CVE-2026-19879

5.3 · MEDIUM

A flaw was found in Undertow, an HTTP server, within its HTTP response header writing path.

Published Aug 14, 2026CWE-681EPSS 0.39%

Overview

CVE-2026-19879 is a medium-severity vulnerability. It was published on August 14, 2026 and has a CVSS 3.1 base score of 5.3 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refaccess.redhat.com/security/cve/CVE-2026-19879Refbugzilla.redhat.com/show_bug.cgi?id=2516038

How CyberStrike helps

Frequently asked questions

What is CVE-2026-19879?

CVE-2026-19879 is a medium-severity vulnerability. It was published on August 14, 2026 and has a CVSS 3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-19879?

This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-19879?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-19879?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-19879 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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