CVE-2026-39972

7.1 HIGH 0.3% exploit odds Fix listed Other

What it is

Mercure is a protocol for pushing data updates to web browsers and other HTTP clients in a battery-efficient way. Prior to 0.22.0, 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. This vulnerability is fixed in 0.22.0.

At a glance

Exploitability: Can be exploited over the network with a low-privilege account. High risk of data exposure.
Exploit odds: 0.3% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-04-09 17:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-10-26 21:10 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.3% in the next 30 days (EPSS).
Severity: 7.1 HIGH (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-04-09 17:16 UTC
Last modified: 2026-10-26 21:10 UTC
Exploit probability: 0.3% · EPSS, next 30 days
Weakness: CWE-1289
Record status: Deferred

Attack profile CVSS 4.0 · 7.1

Attack vector: Network
Complexity: Low
Attack requirements: None
Privileges needed: Low
User interaction: None
Confidentiality: High
Integrity: None
Availability: Low

Raw vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Is it in your code?

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Fix and advisories

References

NVD record · CVE.org record