CVE-2013-6890

medium

Published 2013-12-23 · Modified 2026-04-29

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CVSS v3

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CVSS v4 NEW

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not yet in upstream

VIR risk

6.0

Description

denyhosts 2.6 uses an incorrect regular expression when analyzing authentication logs, which allows remote attackers to cause a denial of service (incorrect block of IP addresses) via crafted login names.

Predictions

Exploit likelihood

20%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

Exploits

Public proof-of-concept code below. AS-IS, for defenders and authorised testing only.

Exploit-DB

EDB-38909 dos linux verified text · 1 KB

Helmut Grohne · 2013-12-19

DenyHosts - 'regex.py' Remote Denial of Service

text exploit Source: Exploit-DB

source: https://www.securityfocus.com/bid/64478/info

DenyHosts is prone to a remote denial-of-service vulnerability.

Successfully exploiting this issue allows remote attackers to deny further SSH network access to arbitrary IP addresses, denying service to legitimate users. 

ssh -l 'Invalid user root from 123.123.123.123' 21.21.21.21

OS impact

Debian Affected 3 releases

Version	Status	Fixed in
7.1	Affected	—
7.0	Affected	—
6.0	Affected	—

Fedora Affected 1 release

Version	Status	Fixed in
—	Affected	—

Application impact

Vendor	Product	Versions	Fixed
phil_schwartz	denyhosts	`2.6`

References

CWEs

CWE-287

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.