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GHSA-hwr4-mq23-wcv5
No affected components available
Impact
A cache key collision vulnerability in TopicSelectorStore allows an attacker to poison the match result cache, potentially causing private updates to be delivered to unauthorized subscribers or blocking delivery to authorized ones.
The cache key was constructed by concatenating the topic selector and topic with an underscore separator:
k = "m_" + topicSelector + "_" + topic
Because both topic selectors and topics can contain underscores, two distinct pairs can produce the same key:
selector="foo_bar" topic="baz" → key: "m_foo_bar_baz"
selector="foo" topic="bar_baz" → key: "m_foo_bar_baz"
An attacker who can subscribe to the hub or publish updates with crafted topic names can exploit this to bypass authorization checks on private updates.
Patches
The vulnerability is fixed by replacing string-encoded cache keys with typed Go struct keys that are inherently collision-free:
type matchCacheKey struct {
topicSelector string
topic string
}
The internal TopicSelectorStoreCache interface and sharded cache abstraction have also been removed in favor of a single typed otter cache.
Users should upgrade to version 0.22.0 or later.
Workarounds
Disable the topic selector cache by setting topic_selector_cache to -1 in the Caddyfile, or by passing a cache size of 0 when using the library directly. This eliminates the vulnerability at the cost of reduced performance.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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