High, CVSS 7.1GoPublished
mercure has Topic Selector Cache Key Collision
CVE-2026-39972 · GHSA-hwr4-mq23-wcv5
- Affected
- Go github.com/dunglas/mercure < 0.22.0
- Fixed in
- 0.22.0· Vendor fix available
- Issue
- 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: Because both topic selectors and topics can contain underscores, two distinct pairs can produce the same key: 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: 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…
Recommended action: Upgrade to 0.22.0 or later, then redeploy and verify.A vendor fix does not resolve your finding until you verify it in your own systems.