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DenyHosts: Denial of Service


1.  Gentoo Linux Security Advisory

Version Information

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


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

2.  Impact Information


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


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


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


There is no known workaround at this time.


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


Page updated October 13, 2007

Summary: This is a Gentoo Linux Security Advisory

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