CVE-2026-21439: badkeys is a tool and library for checking cryptographic public keys for known vulnerabilities

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MEDIUM 5.3REMOTEUPGRADE

CVE-2026-21439 is a medium-severity flaw (CVSS 5.3) affecting badkeys. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 74%)
CISA exploited list	No
Weakness	CWE-150
Published	2026-01-06
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: badkeys

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-01-06 00:15 UTCPublished CVE record published
2026-06-17 10:18 UTCUpdated Record last modified

badkeys badkeys UPGRADE

Affected: < 0.0.16

Fixed in: 0.0.16

Safe to downgrade to: no unaffected older release

1. Check installed version

pip show badkeys

2. UPGRADE to 0.0.16

pip install --upgrade "badkeys>=0.0.16"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-21439?

badkeys: upgrade to 0.0.16. Exact commands for each OS are on this page.

Is CVE-2026-21439 being exploited?

CVE-2026-21439 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-21439 affect?

CVE-2026-21439 affects badkeys. Severity is medium (CVSS 5.3). 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

How urgent is CVE-2026-21439?

Priority 35/100. Public exploit reference; Remotely exploitable, no login, no user action

References

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