{"id":"ALPINE-CVE-2021-21404","details":"Syncthing is a continuous file synchronization program. In Syncthing before version 1.15.0, the relay server `strelaysrv` can be caused to crash and exit by sending a relay message with a negative length field. Similarly, Syncthing itself can crash for the same reason if given a malformed message from a malicious relay server when attempting to join the relay. Relay joins are essentially random (from a subset of low latency relays) and Syncthing will by default restart when crashing, at which point it's likely to pick another non-malicious relay. This flaw is fixed in version 1.15.0.","modified":"2026-11-03T06:32:31.743923686Z","published":"2021-04-06T20:15:13.490Z","upstream":["CVE-2021-21404"],"references":[{"type":"ADVISORY","url":"https://security.alpinelinux.org/vuln/CVE-2021-21404"}],"affected":[{"package":{"name":"syncthing","ecosystem":"Alpine:v3.13","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.12.1-r1"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.14","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.15","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.16","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.17","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.18","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.19","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.20","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.21","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.22","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.23","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}},{"package":{"name":"syncthing","ecosystem":"Alpine:v3.24","purl":"pkg:apk/alpine/syncthing?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.15.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2021-21404.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}