Projects/Audit

This is an early stage project for MIT Kerberos. It is being fleshed out by its proponents. Feel free to help flesh out the details of this project. After the project is ready, it will be presented for review and approval.

Purpose

The focus of this project will be on creating an Audit infrastructure within MIT Kerberos to monitor security related events on the KDC. The initial set of the audible events will be identified.

Requirements

The new audit system should be:

• build-time enabled;
• run-time pluggable;
• simple, so it could be easily replaced with the OS specific implementations;
• if possible, prepare i18n- and l10n-ready log messages.

Events

This section details the categories of the auditable events and the associated information.

Audit module loaded/unloaded

Startup and shutdown of the audit system must be recorded by audit system;

KDC started/stopped

KDC startup - KDC clockskew, list of realms and ports, location and names of the plugins, the values of allow_weak_crypto, kdc_req_sumtype, default_ap_req_sumtype and default_safe_sumtype from configuration files;

KDC stopped - no additional information;

AS exchange

kdc time timestamps,client's and server's flags and unparsed names, port number, ticket start, end and renew until times and flags, requested enckey types and used session enckey type, pre-auth type requested and used, KDC status message;

TGS exchange

Successful or unsuccessful attempt - kdc time timestamps, unparsed client, server, 2nd client and s4u names, port number, client's enckey types and flags, used session enckey type, is referral, KDC status message;

Alternative TGS;

Cross-realm TGS;

U2U TGS

Session keys

AS and TGS exchange session key generation;

AS and TGS exchange session key cleaning;

Policy

Policies violation when processing requests - TBD;

Design details

Pluggable interface

/* Audit plugin vtable */
typedef struct krb5_audit_vtable_st {
   /* Mandatory: name of module. */
   char *name;
   kau_open_fn  open;
   kau_close_fn  close;
   kau_kdc_start_fn  kdc_start;
   kau_kdc_stop_fn  kdc_stop;
   kau_as_req_fn  as_req;
   kau_tgs_fn  tgs;
   kau_tgs_alt_fn  tgs_alt;
   kau_tgs_u2u_fn  tgs_u2u;
   kau_tgs_xrealm_fn tgs_xrealm;
   kau_sesskey_as_generated_fn  sesskey_as_generated;
   kau_sesskey_as_cleared_fn    sesskey_as_cleared;
   kau_sesskey_tgs_generated_fn sesskey_tgs_generated;
   kau_sesskey_tgs_cleared_fn   sesskey_tgs_cleared;
} *krb5_audit_vtable;

typedef krb5_error_code
(*kau_open_fn)(krb5_context context , kau_ctx *au_ctx);

typedef krb5_error_code
(*kau_close_fn)(krb5_context context, kau_ctx au_ctx);

typedef krb5_error_code
(*kau_kdc_stop_fn)(krb5_context context, kau_ctx au_ctx, krb5_error_code  status);

typedef krb5_error_code
(*kau_kdc_start_fn)(krb5_context context, kau_ctx au_ctx,
                   krb5_deltat clockskew, const char *realm_port,
                   krb5_boolean allow_weak_crypto,
                   const char *plugins, const char *plugin_dir,
                   krb5_cksumtype kdc_req_sumtype,
                   krb5_cksumtype default_ap_req_sumtype,
                   krb5_cksumtype default_safe_sumtype, int status);

typedef krb5_error_code
(*kau_as_req_fn)(krb5_context context, kau_ctx au_ctx,
                  krb5_timestamp kdc_time,  const char *kdc_status,
                  const char *cname, const char *sname,
                  krb5_flags c_flags, krb5_flags s_flags,
                  int req_patype, const int from_port,
                  const char *ktypes krb5_enctype sesskey_etype,
                  krb5_flags tkt_flags,
                  krb5_deltat tkt_start_time, krb5_deltat tkt_end_time, krb5_deltat tkt_renew_till,
                  const char *tkt_cname, const int tr_type, int rep_patype, int status);

typedef krb5_error_code
(*kau_tgs_fn)(krb5_context context, kau_ctx au_ctx,
              krb5_timestamp kdc_time, const char *status_msg,
              const char *cname, const char *sname,
              const char *altcname, const char *s4u_name,
              krb5_flags c_flags, krb5_flags s_flags,
              const int from_port, 
              const char * ktypes_buf, krb5_enctype session_key_etype,
              const int is_referral, int status);

typedef krb5_error_code
(*kau_tgs_alt_fn)(krb5_context context, kau_ctx au_ctx,
                  krb5_timestamp kdc_time, const char *kdc_status,
                  const char *cname, const char *sname,
                  krb5_flags c_flags, krb5_flags s_flags,
                  const int from_port, const char *altsrv, int status);

typedef krb5_error_code
(*kau_tgs_u2u_fn)(krb5_context context, kau_ctx au_ctx,
                  krb5_timestamp kdc_time, const char *kdc_status,
                  const char *cname, const char *sname,
                  krb5_flags c_flags, krb5_flags s_flags,
                  const int from_port, const char *cl2, int status);

typedef krb5_error_code
(*kau_tgs_xrealm_fn)(krb5_context context, kau_ctx au_ctx,
                     krb5_timestamp kdc_time, const char *kdc_status,
                     const char *cname, const char *sname,
                     krb5_flags c_flags, krb5_flags s_flags,
                     const int from_port, const char *xrealmsrv, int status);

typedef krb5_error_code
(*kau_sesskey_as_generated_fn)(krb5_context context, kau_ctx au_ctx,
                              krb5_timestamp kdc_time, const char *kdc_status,
                              const char *cname, const char *sname,
                              const int from_port, const char * ktypes,
                              krb5_enctype used_ktype, int status);

typedef krb5_error_code
(*kau_sesskey_as_cleared_fn)(krb5_context context, kau_ctx au_ctx,
                            krb5_timestamp kdc_time, const char *kdc_status,
                            const char *cname, const char *sname,
                            const int from_port, krb5_enctype used_ktype,int status);

typedef krb5_error_code
(*kau_sesskey_tgs_generated_fn)(krb5_context context, kau_ctx au_ctx,
                              krb5_timestamp kdc_time, const char *kdc_status,
                              const char *cname, const char *sname,
                              const int from_port,
                              const char *ktypes, krb5_enctype used_ktype, int status);

typedef krb5_error_code
(*kau_sesskey_tgs_cleared_fn)(krb5_context context, kau_ctx au_ctx,
                             krb5_timestamp kdc_time, const char *kdc_status,
                             const char *cname, const char *sname,
                             const int from_port, krb5_enctype used_ktype, int status);
                                                                       

API signatures

/* Audit plugin loaded/unloaded */
krb5_error_code 
load_audit_plugin(krb5_context context);
krb5_error_code 
unload_audit_plugin(krb5_context context);

/* KDC started /stopped */
krb5_error_code 
kau_kdc_start(krb5_context context, int status);
krb5_error_code 
kau_kdc_stop(krb5_context context, krb5_error_code status);

/* AS exchange: Successful or unsuccessful attempt */
krb5_error_code 
kau_as_req(krb5_context context,
           struct as_req_state *state, int status);

/* TGS exchange: Successful or unsuccessful attempt; alternative, u2u and cross-realm TGS */
krb5_error_code 
kau_tgs(krb5_context context,
        struct tgs_req_audit_state *state, int status);
krb5_error_code 
kau_tgs_alt(krb5_context context,
            struct tgs_req_audit_state *state, int status);
krb5_error_code
kau_tgs_u2u(krb5_context context, struct tgs_req_audit_state *state,
            krb5_principal cl2, int status);
krb5_error_code
kau_tgs_xrealm(krb5_context context, struct tgs_req_audit_state *state,
               krb5_principal xrealmtgt, int status);

/* Session key generation and cleaning them up */
krb5_error_code 
kau_sesskey_as_generated(krb5_context context,
                         struct as_req_state *state, int status);
krb5_error_code 
kau_sesskey_as_cleared(krb5_context context,
                       struct as_req_state *state, int status);
krb5_error_code 
kau_sesskey_tgs_generated(krb5_context context,
                          struct tgs_req_audit_state *state,int status);
krb5_error_code 
kau_sesskey_tgs_cleared(krb5_context context,
                        struct tgs_req_audit_state *state, int status);

/* Policy driven events - TBD */
krb5_error_code 
kau_policy(krb5_context context, ... , krb5_error_code status);

/* Name of audit module */
krb5_error_code 
kau_plugin_name(krb5_context context, char **name);

Configuration

The following ./configure options are added:

--enable-audit[=yes/no]

Enable audit plugin. By default at build time audit is disabled.

--with-audit-plugin=simple

(For demo and testing purposes) Build the audit plugin "simple" and enable audit plugin.

Test implementation

We will use libaudit module available on Fedora, Debian, Suse for the first round.

Some "simple" audit plugin will be implemented and Python test system will become aware of its existence. New ./configure --with-audit-plugin option will be introduced to build "simple" audit plugin for testing purpose. If audit is enabled and audit plugin is available, "make check" will store audit messages into audit log file.

References

1. Common Criteria for Information Technology Security Evaluation http://www.commoncriteriaportal.org/files/ccfiles/CCPART2V3.1R4.pdf
2. Oracle Solaris Auditing http://docs.oracle.com/cd/E19963-01/html/821-1456/auditov-1.html
3. Understanding Linux Audit http://doc.opensuse.org/products/draft/SLES/SLES-security_sd_draft/cha.audit.comp.html
4. Advanced Security Audit Policy Settings http://technet.microsoft.com/en-us/library/dd772712(v=ws.10).aspx
5. Events Classification in Log Audit http://airccse.org/journal/nsa/0410ijnsa5.pdf