Description
sshd in OpenSSH before 4.4, when using the version 1 SSH protocol, allows remote attackers to cause a denial of service (CPU consumption) via an SSH packet that contains duplicate blocks, which is not properly handled by the CRC compensation attack detector.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | openssh | 1:4.3p2-4 | — |
| Debian 13 | openssh | 1:4.3p2-4 | — |
| Debian 12 | openssh | 1:4.3p2-4 | — |
| Debian 3.1 | openssh | 1:3.8.1p1-8.sarge.6 | DSA-1212-1 |
| Debian 3.1 | openssh-krb5 | 3.8.1p1-7sarge1 | DSA-1189-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 4 | openssh +4 | 3.9p1-8.RHEL4.17 | RHSA-2006:0697 |
| RHEL 3 | openssh +4 | 3.6.1p2-33.30.12 | RHSA-2006:0697 |
| RHEL 2 | openssh +4 | 3.1p1-21 | RHSA-2006:0698 |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
Third-party code, not reviewed by us. Public PoCs are sometimes fake or contain malware. Read the code first and run it only in an isolated lab, against systems you are authorised to test.
Exploit-DB 1
- OpenSSH 4.3 p1 - Duplicated Block Remote Denial of Service EDB-2444 · dos · Sep 27, 2006 · verified
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Advisories 4
- RHSA-2006:0697 Red Hat Security Advisory: openssh security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- RHSA-2006:0698 Red Hat Security Advisory: openssh security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- DSA-1212-1 openssh Debian Security (DSA / DLA) · Mar 9, 2026
- DSA-1189-1 openssh-krb5 Debian Security (DSA / DLA) · Mar 9, 2026
References
- FreeBSD-SA-06:22 vendor-advisory
- http://sourceforge.net/forum/forum.php?forum_id=681763
- http://blogs.sun.com/security/entry/sun_alert_102962_security_vulnerability
- 22270 third-party-advisory
- HPSBUX02178 vendor-advisory
- 23038 third-party-advisory
- USN-355-1 vendor-advisory
- 2006-0054 vendor-advisory
- http://www.vmware.com/support/vi3/doc/esx-3069097-patch.html
- ADV-2006-4401 vdb-entry
- http://sourceforge.net/project/shownotes.php?release_id=461863&group_id=69227
- ADV-2009-0740 vdb-entry
- 22116 third-party-advisory
- 21923 third-party-advisory
- 24805 third-party-advisory
- 23340 third-party-advisory
- [2.9] 015: SECURITY FIX: October 12, 2006 vendor-advisory
- SUSE-SR:2006:024 vendor-advisory
- 22487 third-party-advisory
- TA07-072A third-party-advisory
- GLSA-200611-06 vendor-advisory
- http://support.avaya.com/elmodocs2/security/ASA-2006-262.htm
- http://bugs.gentoo.org/show_bug.cgi?id=148228
- 22164 third-party-advisory
- 102962 vendor-advisory
- SUSE-SA:2006:062 vendor-advisory
- 22362 third-party-advisory
- 23680 third-party-advisory
- APPLE-SA-2007-03-13 vendor-advisory
- 34274 third-party-advisory
- VU#787448 third-party-advisory
- http://docs.info.apple.com/article.html?artnum=305214
- 1016931 vdb-entry
- ADV-2006-4869 vdb-entry
- 22298 third-party-advisory
- 22352 third-party-advisory
- 22236 third-party-advisory
- oval:org.mitre.oval:def:1193 vdb-entry signature
- 24799 third-party-advisory
- https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=207955
- 22091 third-party-advisory
- 22495 third-party-advisory
- ADV-2007-1332 vdb-entry
- 20216 vdb-entry
- 20060927 rPSA-2006-0174-1 gnome-ssh-askpass openssh openssh-client openssh-server mailing-list
- GLSA-200609-17 vendor-advisory
- 22823 third-party-advisory
- SSA:2006-272-02 vendor-advisory
- RHSA-2006:0697 vendor-advisory
- https://hypersonic.bluecoat.com/support/securityadvisories/ssh_server_on_sg
- ADV-2006-3777 vdb-entry
- OpenPKG-SA-2006.022 vendor-advisory
- 22183 third-party-advisory
- openssh-block-dos(29158) vdb-entry
- [openssh-unix-dev] 20060927 Announce: OpenSSH 4.4 released mailing-list
- 23241 third-party-advisory
- ADV-2007-2119 vdb-entry
- ADV-2007-0930 vdb-entry
- [security-announce] 20070409 Globus Security Advisory 2007-02: GSI-OpenSSH vulnerability mailing-list
- 22926 third-party-advisory