diff options
Diffstat (limited to 'repo/heimdal/CVE-2018-16860.patch')
| -rw-r--r-- | repo/heimdal/CVE-2018-16860.patch | 147 |
1 files changed, 0 insertions, 147 deletions
diff --git a/repo/heimdal/CVE-2018-16860.patch b/repo/heimdal/CVE-2018-16860.patch deleted file mode 100644 index 6424b9e..0000000 --- a/repo/heimdal/CVE-2018-16860.patch +++ /dev/null @@ -1,147 +0,0 @@ -From c6257cc2c842c0faaeb4ef34e33890ee88c4cbba Mon Sep 17 00:00:00 2001 -From: Isaac Boukris <iboukris@gmail.com> -Date: Tue, 14 May 2019 09:03:18 -0400 -Subject: [PATCH] CVE-2018-16860 Heimdal KDC: Reject PA-S4U2Self with unkeyed - checksum - -S4U2Self is an extension to Kerberos used in Active Directory to allow -a service to request a kerberos ticket to itself from the Kerberos Key -Distribution Center (KDC) for a non-Kerberos authenticated user -(principal in Kerboros parlance). This is useful to allow internal -code paths to be standardized around Kerberos. - -S4U2Proxy (constrained-delegation) is an extension of this mechanism -allowing this impersonation to a second service over the network. It -allows a privileged server that obtained a S4U2Self ticket to itself -to then assert the identity of that principal to a second service and -present itself as that principal to get services from the second -service. - -There is a flaw in Samba's AD DC in the Heimdal KDC. When the Heimdal -KDC checks the checksum that is placed on the S4U2Self packet by the -server to protect the requested principal against modification, it -does not confirm that the checksum algorithm that protects the user -name (principal) in the request is keyed. This allows a -man-in-the-middle attacker who can intercept the request to the KDC to -modify the packet by replacing the user name (principal) in the -request with any desired user name (principal) that exists in the KDC -and replace the checksum protecting that name with a CRC32 checksum -(which requires no prior knowledge to compute). - -This would allow a S4U2Self ticket requested on behalf of user name -(principal) user@EXAMPLE.COM to any service to be changed to a -S4U2Self ticket with a user name (principal) of -Administrator@EXAMPLE.COM. This ticket would then contain the PAC of -the modified user name (principal). - -================== -CVSSv3 calculation -================== - -CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H (7.5) - -========================= -Workaround and Mitigation -========================= - -If server does not take privileged actions based on Kerberos tickets -obtained by S4U2Self nor obtains Kerberos tickets via further -S4U2Proxy requests then this issue cannot be exploited. - -Note that the path to an exploit is not generic, the KDC is not harmed -by the malicious checksum, it is the client service requesting the -ticket being mislead, because it trusted the KDC to return the correct -ticket and PAC. - -It is out of scope for Samba to describe all of the possible tool -chains that might be vulnerable. Here are two examples of possible -exploits in order to explain the issue more clearly. - -1). SFU2Self might be used by a web service authenticating an end user -via OAuth, Shibboleth, or other protocols to obtain a S4U2Self -Kerberos service ticket for use by any Kerberos service principal the -web service has a keytab for. One example is acquiring an AFS token -by requesting an afs/cell@REALM service ticket for a client via -SFU2Self. With this exploit an organization that deploys a KDC built -from Heimdal (be it Heimdal directly or vendor versions such as found -in Samba) is vulnerable to privilege escalation attacks. - -2). If a server authenticates users using X509 certificates, and then -uses S4U2Self to obtain a Kerberos service ticket on behalf of the -user (principal) in order to authorize access to local resources, a -man-in-the-middle attacker could allow a non-privilaged user to access -privilaged resources being protected by the server, or privilaged -resources being protected by a second server, if the first server uses -the S4U2Proxy extension in order to get a new Kerberos service ticket -to obtain access to the second server. - -In both these scenarios under conditions allowing man-in-the-middle -active network protocol manipulation, a malicious user could -authenticate using the non-Kerborized credentials of an unprivileged -user, and then elevate its privileges by intercepting the packet from -the server to the KDC and changing the requested user name (principal). - -The only Samba clients that use S4U2Self are: - -- the "net ads kerberos pac dump" (debugging) tool. - -- the CIFS proxy in the deprecated/developer-only NTVFS file -server. Note this code is not compiled or enabled by default. - -In particular, winbindd does *not* use S4U2Self. - -Finally, MIT Kerberos and so therefore the experimental MIT KDC backend -for Samba AD is understood not to be impacted. - -=============== -Further Reading -=============== - -There is more detail on and a description of the protocols in - -[MS-SFU]: Kerberos Protocol Extensions: Service for User and Constrained -Delegation Protocol -https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-sfu/ - -======= -Credits -======= - -Originally reported by Isaac Boukris and Andrew Bartlett of the Samba -Team and Catalyst. - -Patches provided by Isaac Boukris. - -Advisory written by Andrew Bartlett of the Samba Team and Catalyst, -with contributions from Isaac Boukris, Jeffrey Altman and Jeremy -Allison. - -BUG: https://bugzilla.samba.org/show_bug.cgi?id=13685 -Change-Id: I4ac69ebf0503eb999a7d497a2c30fe4d293a8cc8 -Signed-off-by: Isaac Boukris <iboukris@gmail.com> -Reviewed-by: Andrew Bartlett <abartlet@samba.org> -Signed-off-by: Andrew Bartlett <abartlet@samba.org> -Reviewed-by: Jeffrey Altman <jaltman@auristor.com> -Signed-off-by: Jeffrey Altman <jaltman@auristor.com> ---- - kdc/krb5tgs.c | 7 +++++++ - 1 file changed, 7 insertions(+) - -diff --git a/kdc/krb5tgs.c b/kdc/krb5tgs.c -index 8318bc0025..14943077a4 100644 ---- a/kdc/krb5tgs.c -+++ b/kdc/krb5tgs.c -@@ -2031,6 +2031,13 @@ tgs_build_reply(krb5_context context, - goto out; - } - -+ if (!krb5_checksum_is_keyed(context, self.cksum.cksumtype)) { -+ free_PA_S4U2Self(&self); -+ kdc_log(context, config, 0, "Reject PA-S4U2Self with unkeyed checksum"); -+ ret = KRB5KRB_AP_ERR_INAPP_CKSUM; -+ goto out; -+ } -+ - ret = _krb5_s4u2self_to_checksumdata(context, &self, &datack); - if (ret) - goto out; |