Public bug reported:
Background:
Under some circumstances, when the client/initiator has a TGT but no
ticket for a particular principal, it needs to communicate with the KDC.
The GSSAPI protocol includes a mechanism, a subprotocol named IAKERB,
for the client to tunnel/proxy through the server/acceptor instead of
directly communicating with the KDC. (This is useful if e.g. the GSSAPI
initiator does not have full network access but the acceptor does.)
Problem:
The formatting of the IAKERB messages is incorrect. Every draft of the
IAKERB protocol I have been able to find defines the IAKERB-HEADER
structure to have a field "Realm" which is a UTF8String, like this:
IAKERB-HEADER ::= SEQUENCE {
target-realm [1] UTF8String,
However, observed protocol exchanges tag the Realm field as an OCTET
STRING.
I believe the bug is in src/lib/krb5/asn.1/asn1_k_encode.c near line
1146, where the DEFFIELD(iakerb_header_1,...) macro is invoked with
"ostring_data". I think it should be invoked with "utf8_data" instead.
Reproduction:
I observed this using Firefox attempting to authenticate with a webserver using
the "Negotiate" protocol. The first Negotiate message from the browser to the
server contains:
GSSAPI token (RFC2743 3.3); mechanism 1.3.6.1.5.5.2 (SPNEGO)
innerToken is a NegTokenInit (RFC4178 4.2.1)
mech = 1.3.6.1.5.2.5 (IAKERB)
mechToken is a (wrapped) GSSAPI token (RFC2743 again) with mech =
1.3.6.1.5.2.5
innerToken is the concatenation of:
TOK_ID 05 01 (IAKERB)
IAKERB-HEADER
a Kerberos TGS-REQ
Dumping the IAKERB-HEADER with `openssl asnparse` produces:
0:d=0 hl=2 l= 12 cons: SEQUENCE
2:d=1 hl=2 l= 10 cons: cont [ 1 ]
4:d=2 hl=2 l= 8 prim: OCTET STRING :HHHH.ORG
As you can see the realm (HHHH.ORG) is tagged as OCTET STRING, rather
than being tagged as UTF8String.
Versions:
Description: Ubuntu 16.04.5 LTS
Release: 16.04
libgssapi-krb5-2:
Installed: 1.13.2+dfsg-5ubuntu2
Candidate: 1.13.2+dfsg-5ubuntu2
Version table:
*** 1.13.2+dfsg-5ubuntu2 500
500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64
Packages
100 /var/lib/dpkg/status
1.13.2+dfsg-5 500
500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
** Affects: krb5 (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1793594
Title:
IAKERB-HEADER "Realm" field incorrectly encoded as OCTET STRING
Status in krb5 package in Ubuntu:
New
Bug description:
Background:
Under some circumstances, when the client/initiator has a TGT but no
ticket for a particular principal, it needs to communicate with the
KDC. The GSSAPI protocol includes a mechanism, a subprotocol named
IAKERB, for the client to tunnel/proxy through the server/acceptor
instead of directly communicating with the KDC. (This is useful if
e.g. the GSSAPI initiator does not have full network access but the
acceptor does.)
Problem:
The formatting of the IAKERB messages is incorrect. Every draft of the
IAKERB protocol I have been able to find defines the IAKERB-HEADER
structure to have a field "Realm" which is a UTF8String, like this:
IAKERB-HEADER ::= SEQUENCE {
target-realm [1] UTF8String,
However, observed protocol exchanges tag the Realm field as an OCTET
STRING.
I believe the bug is in src/lib/krb5/asn.1/asn1_k_encode.c near line
1146, where the DEFFIELD(iakerb_header_1,...) macro is invoked with
"ostring_data". I think it should be invoked with "utf8_data" instead.
Reproduction:
I observed this using Firefox attempting to authenticate with a webserver
using the "Negotiate" protocol. The first Negotiate message from the browser to
the server contains:
GSSAPI token (RFC2743 3.3); mechanism 1.3.6.1.5.5.2 (SPNEGO)
innerToken is a NegTokenInit (RFC4178 4.2.1)
mech = 1.3.6.1.5.2.5 (IAKERB)
mechToken is a (wrapped) GSSAPI token (RFC2743 again) with mech =
1.3.6.1.5.2.5
innerToken is the concatenation of:
TOK_ID 05 01 (IAKERB)
IAKERB-HEADER
a Kerberos TGS-REQ
Dumping the IAKERB-HEADER with `openssl asnparse` produces:
0:d=0 hl=2 l= 12 cons: SEQUENCE
2:d=1 hl=2 l= 10 cons: cont [ 1 ]
4:d=2 hl=2 l= 8 prim: OCTET STRING :HHHH.ORG
As you can see the realm (HHHH.ORG) is tagged as OCTET STRING, rather
than being tagged as UTF8String.
Versions:
Description: Ubuntu 16.04.5 LTS
Release: 16.04
libgssapi-krb5-2:
Installed: 1.13.2+dfsg-5ubuntu2
Candidate: 1.13.2+dfsg-5ubuntu2
Version table:
*** 1.13.2+dfsg-5ubuntu2 500
500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64
Packages
100 /var/lib/dpkg/status
1.13.2+dfsg-5 500
500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/krb5/+bug/1793594/+subscriptions
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