DenyHosts: Denial of Service

1. Gentoo Linux Security Advisory

Advisory Reference	GLSA 200710-14 / denyhosts
Release Date	October 13, 2007
Latest Revision	October 13, 2007: 01
Impact	normal
Exploitable	remote

Package	Vulnerable versions	Unaffected versions	Architecture(s)
app-admin/denyhosts	< 2.6-r1	>= 2.6-r1	All supported architectures

Related bugreports: #181213

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

Daniel B. Cid discovered that DenyHosts used an incomplete regular expression to parse failed login attempts, a different issue than GLSA 200701-01.

Impact

A remote unauthenticated attacker can add arbitrary hosts into the blacklist, including the "all" keyword, by submitting specially crafted version identification strings to the SSH server banner. 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-r1"

4. References

CVE-2007-4323

Page updated October 13, 2007

Summary: This is a Gentoo Linux Security Advisory

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