> The explanation misses a lot of details.
Here's my understanding (only from the article, YMMV):
0. Assume that there is an "admin" account with special power, and that
the attacker has created an "admin99" account.
1. The attacker successfully logs in via a form, and the server sends her
the cookie "admin99|20080601|DEADBEEF". (Assume that md5
("admin9920080601secret") == "DEADBEEF".)
2. On subsequent requests the attacker presents the above cookie. The
server notices that the cookie is valid (because md5
("admin9920080601secret") == "DEADBEEF"), that this is user "admin99",
and that the session has not yet expired (it's still May 2008). Fine!
3. But now the attacker sends the following doctored cookie: "admin|
9920080601|DEADBEEF". This still checks out as valid because md5
("admin9920080601secret") == "DEADBEEF"), the session is for some
reason still not considered expired, so the attacker now has the
identity of user "admin".
 IMO not validating the expiration date format is one of the main
errors here. Or does WP strive to be Y10K compliant??