Description
Shlink through 5.1.6 fails to enforce API key role restrictions when issuing Mercure subscription tokens, allowing restricted keys to subscribe to all topics. Attackers with author-only or domain-only keys can access the mercure-info endpoint to receive visit data including referrer, user agent, geolocation, and full short URL objects for URLs outside their authorization boundary.
References6
Metrics
- CVSS 3.1
-
6.5
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - CVSS 4.0
-
7.1
HIGH
Score source: CNA
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/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 - EPSS — exploit probability
- 0% percentile: 36 · as of 8 November 2026
- CWE
- CWE-863
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.