On Jan 24, 2006, at 2:44 PM, Stephen Farrell wrote:
Douglas Otis wrote:
---[C: Unreasonable estimate of impact from a highly probable
exploit.]
,---
| 4.1. Attacks Against Message Signatures
| ...
| Signed message replay | Low | High |
'---
This should read:
: Signed message replay | Very High | High |
How was this problem rated?
I guess Jim just used his judgment in the expectation that the WG
will review and come to consensus - which is quite the proper thing
to be doing IMO.
Also - there's no "Very High", most risk analysis approaches (that
don't try to sell you over-exactness) just use high/medium/low. So
we can interpret you as asking for "High" in the impact column for
4.1.5.
The Very High was used to make a point. Just High would be fine.
Any large domain has a continuous background of abuse being sent.
In some cases, this abuse may represent tens of thousands of
compromised systems. Any list-server is also prone, as there is
no practical means to screen participants or expect effective
outbound filters when the number of messages do not reflect the
overall traffic until used in the replay. Out of the millions of
valid users within these domains, rate limiting has ensured these
abusive systems represent a smaller percentage of the overall
outbound email in most cases. When used in conjunction with a
replay strategy, rate limits will not remain effective, and yet
the signature still remains valid.
Once the DKIM signature has any acceptance value, expect this
problem to become paramount.
That doesn't make too much sense to me I'm afraid. (But since things
seem to work quicker/better when we do this: let's do it again:-)
Exactly what change are you proposing, other than s/Low/High/ above?
Perhaps the following text could help justify this rating:
: Acceptance based upon the DKIM signature is in jeopardy of
: being exploited for any large domain, a domain offering
: public services, or where the network is exposed. Abusive
: message replay will be able to circumvent containment
: strategies currently used to ensure only tolerable amounts
: of abuse are permitted. Unless there are new strategies
: put in place to deal with this potential exploit, there is
: no reason to expect that DKIM will ever offer a means for
: basing acceptance, as this exploit will affect most domains.
-Doug
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