{
  "guidislink": false,
  "id": "https://tailscale.com/security-bulletins/#ts-2025-006",
  "link": "https://tailscale.com/security-bulletins/#ts-2025-006",
  "links": [
    {
      "href": "https://tailscale.com/security-bulletins/#ts-2025-006",
      "rel": "alternate",
      "type": "text/html"
    }
  ],
  "published": "Tue, 28 Oct 2025 00:00:00 GMT",
  "summary": "\u003cp\u003e\u003cstrong\u003e\u003cem\u003eDescription\u003c/em\u003e\u003c/strong\u003e: A potential access control logic issue affected shared subnet router nodes between tailnets.\u003c/p\u003e\n\u003ch4\u003eWhat happened?\u003c/h4\u003e\n\u003cp\u003eTailscale nodes that are subnet routers and shared with other tailnets did not enforce protocol filters in ACLs. For example, a subnet router with an IP grant of \u003ccode\u003e\"udp:1234\"\u003c/code\u003e in the policy file would allow TCP, UDP, and any other protocol connections to port \u003ccode\u003e1234\u003c/code\u003e. This bug was fixed in our control plane and does not require any update.\u003c/p\u003e\n\u003cp\u003eThe Tailscale Control Plane performs a process known as \u003ca href=\"https://tailscale.com/kb/1087/device-visibility\"\u003enetwork map trimming\u003c/a\u003e to ensure that only nodes with authorized access to each other appear in their respective clients.\u003c/p\u003e\n\u003cp\u003eAs part of this process, the Control Plane transforms ACLs for nodes that serve as \u003ca href=\"https://tailscale.com/kb/1019/subnets\"\u003esubnet routers\u003c/a\u003e, \u003ca href=\"https://tailscale.com/kb/1103/exit-nodes\"\u003eexit node\u003c/a\u003e, or \u003ca href=\"https://tailscale.com/security-bulletins/kb/1281/app-connectors\"\u003eapp connector\u003c/a\u003e and are \u003ca href=\"https://tailscale.com/kb/1084/sharing\"\u003eshared externally\u003c/a\u003e with other tailnets to constrain the access of external tailnet members to only the shared node and prohibit their access to the routed subnets.\u003c/p\u003e\n\u003cp\u003eThis filtering contained a bug, producing ACLs for these nodes that omitted their IP Protocol number information entirely. This caused those nodes to accept connections using arbitrary protocols from both local and external tailnets the node was shared with. The \u003ccode\u003esrc\u003c/code\u003e/\u003ccode\u003edst\u003c/code\u003e restrictions, as well as port restrictions still applied, so these nodes were not accessible broadly.\u003c/p\u003e\n\u003cp\u003eFor ACL rules that relied on protocol-based filtering, such as \u003ccode\u003eimcp:*\u003c/code\u003e this would have allowed connections from the source using arbitrary protocols to the destination.\u003c/p\u003e\n\u003ch4\u003eWhat was the impact?\u003c/h4\u003e\n\u003cp\u003eLocal and external tailnet members with existing access to subnet routers that were shared externally would have been able to exceed their authorized access and establish connections using arbitrary protocols to these nodes.\u003c/p\u003e\n\u003cp\u003eLocal and external members who were not included in the source of the impacted ACL groups would not have been able to access impacted nodes using these rules.\u003c/p\u003e\n\u003cp\u003eThere is \u003cstrong\u003eno indication of this issue being exploited\u003c/strong\u003e in the wild. The exposure is limited to nodes that were intentionally shared to another tailnet.\u003c/p\u003e\n\u003ch4\u003eWho was affected?\u003c/h4\u003e\n\u003cp\u003eTailnets with nodes that are subnet routers, that were also shared with external tailnets, and whose ACLs for these nodes relied on protocol filtering were affected.\u003c/p\u003e\n\u003cp\u003eThis bug was present in all Tailscale clients from the introduction of these features, and was fixed for all clients through the Tailscale control plane on October 29th 2025.\u003c/p\u003e\n\u003ch4\u003eWhat do I need to do?\u003c/h4\u003e\n\u003cp\u003e\u003cstrong\u003eNo action is required\u003c/strong\u003e. Tailscale has deployed a fix to the control plane as of 2025-10-29.\u003c/p\u003e\n\u003ch4\u003eCredits\u003c/h4\u003e\n\u003cp\u003eWe would like to thank \u003ca href=\"https://www.linkedin.com/in/thariq-shanavas\"\u003eThariq Shanavas\u003c/a\u003e for reporting this issue.\u003c/p\u003e",
  "summary_detail": {
    "base": "https://tailscale.com/security-bulletins/index.xml",
    "language": null,
    "type": "text/html",
    "value": "\u003cp\u003e\u003cstrong\u003e\u003cem\u003eDescription\u003c/em\u003e\u003c/strong\u003e: A potential access control logic issue affected shared subnet router nodes between tailnets.\u003c/p\u003e\n\u003ch4\u003eWhat happened?\u003c/h4\u003e\n\u003cp\u003eTailscale nodes that are subnet routers and shared with other tailnets did not enforce protocol filters in ACLs. For example, a subnet router with an IP grant of \u003ccode\u003e\"udp:1234\"\u003c/code\u003e in the policy file would allow TCP, UDP, and any other protocol connections to port \u003ccode\u003e1234\u003c/code\u003e. This bug was fixed in our control plane and does not require any update.\u003c/p\u003e\n\u003cp\u003eThe Tailscale Control Plane performs a process known as \u003ca href=\"https://tailscale.com/kb/1087/device-visibility\"\u003enetwork map trimming\u003c/a\u003e to ensure that only nodes with authorized access to each other appear in their respective clients.\u003c/p\u003e\n\u003cp\u003eAs part of this process, the Control Plane transforms ACLs for nodes that serve as \u003ca href=\"https://tailscale.com/kb/1019/subnets\"\u003esubnet routers\u003c/a\u003e, \u003ca href=\"https://tailscale.com/kb/1103/exit-nodes\"\u003eexit node\u003c/a\u003e, or \u003ca href=\"https://tailscale.com/security-bulletins/kb/1281/app-connectors\"\u003eapp connector\u003c/a\u003e and are \u003ca href=\"https://tailscale.com/kb/1084/sharing\"\u003eshared externally\u003c/a\u003e with other tailnets to constrain the access of external tailnet members to only the shared node and prohibit their access to the routed subnets.\u003c/p\u003e\n\u003cp\u003eThis filtering contained a bug, producing ACLs for these nodes that omitted their IP Protocol number information entirely. This caused those nodes to accept connections using arbitrary protocols from both local and external tailnets the node was shared with. The \u003ccode\u003esrc\u003c/code\u003e/\u003ccode\u003edst\u003c/code\u003e restrictions, as well as port restrictions still applied, so these nodes were not accessible broadly.\u003c/p\u003e\n\u003cp\u003eFor ACL rules that relied on protocol-based filtering, such as \u003ccode\u003eimcp:*\u003c/code\u003e this would have allowed connections from the source using arbitrary protocols to the destination.\u003c/p\u003e\n\u003ch4\u003eWhat was the impact?\u003c/h4\u003e\n\u003cp\u003eLocal and external tailnet members with existing access to subnet routers that were shared externally would have been able to exceed their authorized access and establish connections using arbitrary protocols to these nodes.\u003c/p\u003e\n\u003cp\u003eLocal and external members who were not included in the source of the impacted ACL groups would not have been able to access impacted nodes using these rules.\u003c/p\u003e\n\u003cp\u003eThere is \u003cstrong\u003eno indication of this issue being exploited\u003c/strong\u003e in the wild. The exposure is limited to nodes that were intentionally shared to another tailnet.\u003c/p\u003e\n\u003ch4\u003eWho was affected?\u003c/h4\u003e\n\u003cp\u003eTailnets with nodes that are subnet routers, that were also shared with external tailnets, and whose ACLs for these nodes relied on protocol filtering were affected.\u003c/p\u003e\n\u003cp\u003eThis bug was present in all Tailscale clients from the introduction of these features, and was fixed for all clients through the Tailscale control plane on October 29th 2025.\u003c/p\u003e\n\u003ch4\u003eWhat do I need to do?\u003c/h4\u003e\n\u003cp\u003e\u003cstrong\u003eNo action is required\u003c/strong\u003e. Tailscale has deployed a fix to the control plane as of 2025-10-29.\u003c/p\u003e\n\u003ch4\u003eCredits\u003c/h4\u003e\n\u003cp\u003eWe would like to thank \u003ca href=\"https://www.linkedin.com/in/thariq-shanavas\"\u003eThariq Shanavas\u003c/a\u003e for reporting this issue.\u003c/p\u003e"
  },
  "title": "TS-2025-006",
  "title_detail": {
    "base": "https://tailscale.com/security-bulletins/index.xml",
    "language": null,
    "type": "text/plain",
    "value": "TS-2025-006"
  }
}