fix: ACL bypass and # wildcard zero-children in MatchTopic - #170
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MatchTopic returned true unconditionally after exhausting filter parts, without checking whether topic parts remained. A literal filter 'allowed' matched publish to 'allowed/secret'. Fix: return elements, len(topicParts) == len(filterParts). The '#' multi-level wildcard path returns early, unaffected. Reported by Team Atlanta.
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Per MQTT 4.7 spec, the '#' multi-level wildcard must match zero or more sublevels.
The bounds check returned false before checking if the filter part was '#'.
Fix: matched = filterParts[i] == '#', only allow zero-children on '#'.
Regular filters and '+' wildcard still require exact level count.
Test: MatchTopic('a/#', 'a') -> true, MatchTopic('a/+', 'a') -> false.
Updated TestCanACL expectation: topic 'updates' is now correctly denied
for read because global rule 'updates/#' (WriteOnly) matches 'updates'
with the zero-children fix.
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#170 - MatchTopic fixes
Fix 1: ACL bypass via prefix topic matching (CVSS 4.3)
Reported by Team Atlanta. MatchTopic returned true unconditionally after exhausting filter parts, without checking whether topic parts remain. A literal filter "allowed" matched publish to "allowed/secret".
Fix: return len(topicParts) == len(filterParts)
Fix 2: # wildcard zero-children matching
Per MQTT 4.7 spec, # must match zero or more child levels. The bounds check returned false before checking if filter part was #, so a/# failed to match a.
Fix: matched = filterParts[i] == "#"
Changes
mqtt/hooks/auth/ledger.go 2+
mqtt/hooks/auth/ledger_test.go 16+
Reported by Team Atlanta.