AUGUST 14, 2026
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Case File

CVE-2026-19879

MEDIUM · CVSS 5.3 Public Exploit

Source: NVD + CISA KEV + EPSS · Published 2026-08-14 · Last synced 2026-08-14

CyberRota Analysis

AI-Generated

Undertow's HTTP server is vulnerable due to a flaw in the `writeString()` method, which improperly narrows 16-bit Unicode characters to 8-bit bytes when writing HTTP response headers. This can allow remote attackers to exploit the vulnerability by injecting specific Unicode characters, leading to potential information disclosure or integrity issues if user input is not adequately sanitized. Organizations using Undertow should prioritize addressing this vulnerability to mitigate risks associated with user-controlled input in response headers.

Public Exploit Signal

A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.

Detected Signals
exploit

Note: these links are listed for security research and verification purposes only.

CVE
CVE-2026-19879
Severity
MEDIUM
CVSS
5.3
EPSS
N/A

Original NVD 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.