SASL is Cyrus's Simple Authentication and Security Layer. And like every other Cyrus project I've seen, its a big mystery.
See SASL for information on what its (supposed) to do. See here for notes on its use.
libsasl has an unfortunate bug in that it is non re-entrant. This has the unfortunate effect of casuing segfaults in applications using libsasl.
I've seen this occur mainly when using libnss-ldap and libpam-ldap coupled with cyrus imapd. The big problem here is that both libldap2 and cyrus imapd's auth module are linked against libsasl - this can cause a chain of events which leads to a double free, which causes the application to die with SIGSEGV (SIG11, segmentation fault)
Solution: recompile libldap2 without cyrus sasl support.
Under Debian:
2 pages link to SASLNotes:
lib/main.php:944: Notice: PageInfo: Cannot find action page