2

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-21439

CVE-2026-21439: badkeys vulnerable to ASCII control character injection on console via malformed input

badkeys is a tool and library for checking cryptographic public keys for known vulnerabilities. In versions 0.0.15 and below, an attacker may inject content with ASCII control characters like vertical tabs, ANSI escape sequences, etc., that can create misleading output of the badkeys command-line tool. This impacts scanning DKIM keys (both --dkim and --dkim-dns), SSH keys (--ssh-lines mode), and filenames in various modes. This issue is fixed in version 0.0.16.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2026-21439

CVE-2026-21439:

2

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
badkeys	pip	<= 0.0.15	0.0.16

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability lies in the direct printing of user-controllable input to the console without proper sanitization. The badkeys command-line tool processes various inputs like DKIM keys, SSH keys, filenames, and hostnames. The analysis of the patches reveals that several functions were printing these inputs directly within informational or warning messages.

The root cause is the lack of escaping for ASCII control characters. An attacker could provide a specially crafted filename, hostname, or key data containing sequences like ANSI escape codes. When the badkeys tool would print a message containing this data, the terminal would interpret these sequences, allowing the attacker to manipulate the console output, hide information, or create misleading results.

The patches address this by introducing a new utility function, _esc, which uses repr() to escape non-printable characters in the input string before it is printed. This sanitization is applied in all identified vulnerable locations within the runcli and dkim modules, effectively neutralizing the injection vector.

Vulnerable functions

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WAF Rule

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Reasoning

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