{"cve":"CVE-2026-39972","nvd":{"published":"2026-04-09T17:16:30.770","modified":"2026-10-26T21:10:00.170","status":"Deferred","description":"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.","cvss_v4":{"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","score":7.1},"cvss_v3":null,"cwes":["CWE-1289"],"references":["https://github.com/dunglas/mercure/commit/4964a69be904fd61e35b5f1e691271663b6fdd64","https://github.com/dunglas/mercure/security/advisories/GHSA-hwr4-mq23-wcv5"],"products":[],"source":"nvd","synced_at":"2026-10-26T21:38:48.864438205+00:00"},"epss":{"cve":"CVE-2026-39972","score":0.00341,"percentile":0.27325,"date":"2026-10-26"},"kev":null,"osv":[{"id":"GHSA-hwr4-mq23-wcv5","url":"https://osv.dev/vulnerability/GHSA-hwr4-mq23-wcv5","summary":"mercure has Topic Selector Cache Key Collision","modified":"2026-09-10T03:51:02.104486366Z","packages":[{"ecosystem":"Go","name":"github.com/dunglas/mercure","purl":"pkg:golang/github.com/dunglas/mercure","ranges":["<0.22.0"],"fixed":["0.22.0"]}]},{"id":"GO-2026-5444","url":"https://osv.dev/vulnerability/GO-2026-5444","summary":"mercure has Topic Selector Cache Key Collision in github.com/dunglas/mercure","modified":"2026-06-25T23:01:10.139029011Z","packages":[{"ecosystem":"Go","name":"github.com/dunglas/mercure","purl":"pkg:golang/github.com/dunglas/mercure","ranges":["<0.22.0"],"fixed":["0.22.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}