From 13377f0b59e28c7e7b7b6fe922f0b1f1e95042f6 Mon Sep 17 00:00:00 2001 From: Douglas Bagnall Date: Fri, 22 Oct 2021 16:03:18 +1300 Subject: [PATCH] CVE-2020-25722 s4/dsdb/samldb: reject SPN with too few/many components BUG: https://bugzilla.samba.org/show_bug.cgi?id=14564 Signed-off-by: Douglas Bagnall Reviewed-by: Andrew Bartlett --- selftest/knownfail.d/ldap_spn | 2 -- source4/dsdb/samdb/ldb_modules/samldb.c | 41 +++++++++++++++++++++++++ 2 files changed, 41 insertions(+), 2 deletions(-) diff --git a/selftest/knownfail.d/ldap_spn b/selftest/knownfail.d/ldap_spn index b7eb6f30e7a..63f9fe02ef7 100644 --- a/selftest/knownfail.d/ldap_spn +++ b/selftest/knownfail.d/ldap_spn @@ -1,3 +1 @@ samba.tests.ldap_spn.+LdapSpnTest.test_spn_dodgy_spns -samba.tests.ldap_spn.+LdapSpnTest.test_spn_one_part_spns_no_slashes_ -samba.tests.ldap_spn.+LdapSpnTest.test_spn_too_many_spn_parts diff --git a/source4/dsdb/samdb/ldb_modules/samldb.c b/source4/dsdb/samdb/ldb_modules/samldb.c index 9385b6f5fe7..ca82396d0a8 100644 --- a/source4/dsdb/samdb/ldb_modules/samldb.c +++ b/source4/dsdb/samdb/ldb_modules/samldb.c @@ -3873,6 +3873,37 @@ static int check_spn_direct_collision(struct ldb_context *ldb, } +static int count_spn_components(struct ldb_val val) +{ + /* + * a 3 part servicePrincipalName has two slashes, like + * ldap/example.com/DomainDNSZones.example.com. + * + * In krb5_parse_name_flags() we don't count "\/" as a slash (i.e. + * escaped by a backslash), but this is not the behaviour of Windows + * on setting a servicePrincipalName -- slashes are counted regardless + * of backslashes. + * + * Accordingly, here we ignore backslashes. This will reject + * multi-slash SPNs that krb5_parse_name_flags() would accept, and + * allow ones in the form "a\/b" that it won't parse. + */ + size_t i; + int slashes = 0; + for (i = 0; i < val.length; i++) { + char c = val.data[i]; + if (c == '/') { + slashes++; + if (slashes == 3) { + /* at this point we don't care */ + return 4; + } + } + } + return slashes + 1; +} + + /* Check that "servicePrincipalName" changes do not introduce a collision * globally. */ static int samldb_spn_uniqueness_check(struct samldb_ctx *ac, @@ -3888,8 +3919,18 @@ static int samldb_spn_uniqueness_check(struct samldb_ctx *ac, } for (i = 0; i < spn_el->num_values; i++) { + int n_components; spn = (char *)spn_el->values[i].data; + n_components = count_spn_components(spn_el->values[i]); + if (n_components > 3 || n_components < 2) { + ldb_asprintf_errstring(ldb, + "samldb: spn[%s] invalid with %u components", + spn, n_components); + talloc_free(tmp_ctx); + return LDB_ERR_CONSTRAINT_VIOLATION; + } + ret = check_spn_direct_collision(ldb, tmp_ctx, spn, -- 2.47.3