DenyHosts: Denial of Service

1. Gentoo Linux Security Advisory

Advisory Reference	GLSA 200701-01 / denyhosts
Release Date	January 03, 2007
Latest Revision	January 03, 2007: 01
Impact	normal
Exploitable	remote

Package	Vulnerable versions	Unaffected versions	Architecture(s)
app-admin/denyhosts	< 2.6	>= 2.6	All supported architectures

Related bugreports: #157163

Synopsis

DenyHosts does not correctly parse log entries, potentially causing a remote Denial of Service.

2. Impact Information

Background

DenyHosts is designed to monitor SSH servers for repeated failed login attempts.

Description

Tavis Ormandy of the Gentoo Linux Security Audit Team discovered that DenyHosts used an incomplete regular expression to parse failed login attempts.

Impact

A remote unauthenticated attacker can add arbitrary hosts to the blacklist by attempting to login with a specially crafted username. An attacker may use this to prevent legitimate users from accessing a host remotely.

3. Resolution Information

Workaround

There is no known workaround at this time.

Resolution

All DenyHosts users should upgrade to the latest version:

Code Listing 3.1: Resolution

# emerge --sync
# emerge --ask --oneshot --verbose ">=app-admin/denyhosts-2.6"

4. References

CVE-2006-6301

Updated January 03, 2007

Summary: This is a Gentoo Linux Security Advisory

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