Cloudanix VulnDB

GHSA-hwr4-mq23-wcv5

High · 7.1

mercure has Topic Selector Cache Key Collision

CVSS

7.1

EPSS

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Published

Apr 8, 2026

CISA due date

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The record

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: ```go 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.

Affected packages

Ecosystem Package Introduced Fixed

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