CVE WatchAug 14, 2026

CVE-2026-19879

A flaw was found in Undertow, an HTTP server, within its HTTP response header writing path. The `writeString()` method performs a silent nar

CVSS

5.3

Medium

EPSS

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KEV

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Exploit Today

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0-100

Published: Aug 14, 2026 · Last modified: Aug 14, 2026 · CWE-681

EPSS · 30d

Not enough EPSS history yet.

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.

Official references

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