I think we have a couple of open questions on this bug in Ubuntu then:
1) Is it fixed upstream?
2) Sam's question: what's the actual impact to Ubuntu users?
Since we can't make progress without these questions answered, and
depending on the answers we might not consider this to be a bug in
Ubuntu at all, I'm marking the Ubuntu bug task Incomplete to make it
clear to everyone what the current situation is. Once these questions
are answered, please feel free to change the bug status back to New.
** Changed in: krb5 (Ubuntu)
Status: New => Incomplete
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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:
Incomplete
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
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