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GHSA-fg35-5rf6-qg3g
GHSA-fg35-5rf6-qg3g

Author: advisory-database[bot]

advisories/github-reviewed/2026/03/GHSA-fg35-5rf6-qg3g/GHSA-fg35-5rf6-qg3g.json

@@ -0,0 +1,140 @@
+{
+  "schema_version": "1.4.0",
+  "id": "GHSA-fg35-5rf6-qg3g",
+  "modified": "2026-03-31T05:19:17Z",
+  "published": "2026-03-25T18:31:53Z",
+  "aliases": [
+    "CVE-2026-27656"
+  ],
+  "summary": "Mattermost allows attackers to take over arbitrary user accounts via overly permissive substring matching flaw",
+  "details": "Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to properly validate user identity in the OpenID {{IsSameUser()}} comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user discovery flow. Mattermost Advisory ID: MMSA-2026-00590",
+  "severity": [
+    {
+      "type": "CVSS_V3",
+      "score": "CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N"
+    }
+  ],
+  "affected": [
+    {
+      "package": {
+        "ecosystem": "Go",
+        "name": "github.com/mattermost/mattermost-server"
+      },
+      "ranges": [
+        {
+          "type": "ECOSYSTEM",
+          "events": [
+            {
+              "introduced": "11.4.0-rc1"
+            },
+            {
+              "fixed": "11.4.1"
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "package": {
+        "ecosystem": "Go",
+        "name": "github.com/mattermost/mattermost-server"
+      },
+      "ranges": [
+        {
+          "type": "ECOSYSTEM",
+          "events": [
+            {
+              "introduced": "11.3.0-rc1"
+            },
+            {
+              "fixed": "11.3.2"
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "package": {
+        "ecosystem": "Go",
+        "name": "github.com/mattermost/mattermost-server"
+      },
+      "ranges": [
+        {
+          "type": "ECOSYSTEM",
+          "events": [
+            {
+              "introduced": "11.2.0-rc1"
+            },
+            {
+              "fixed": "11.2.4"
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "package": {
+        "ecosystem": "Go",
+        "name": "github.com/mattermost/mattermost-server"
+      },
+      "ranges": [
+        {
+          "type": "ECOSYSTEM",
+          "events": [
+            {
+              "introduced": "10.11.0-rc1"
+            },
+            {
+              "fixed": "10.11.12"
+            }
+          ]
+        }
+      ],
+      "database_specific": {
+        "last_known_affected_version_range": "< 10.11.2"
+      }
+    },
+    {
+      "package": {
+        "ecosystem": "Go",
+        "name": "github.com/mattermost/mattermost/server/v8"
+      },
+      "ranges": [
+        {
+          "type": "ECOSYSTEM",
+          "events": [
+            {
+              "introduced": "8.0.0-20260105080200-d27a2195068d"
+            },
+            {
+              "fixed": "8.0.0-20260217110922-b7d4a1f1f59b"
+            }
+          ]
+        }
+      ]
+    }
+  ],
+  "references": [
+    {
+      "type": "ADVISORY",
+      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27656"
+    },
+    {
+      "type": "PACKAGE",
+      "url": "https://github.com/mattermost/mattermost"
+    },
+    {
+      "type": "WEB",
+      "url": "https://mattermost.com/security-updates"
+    }
+  ],
+  "database_specific": {
+    "cwe_ids": [
+      "CWE-303"
+    ],
+    "severity": "MODERATE",
+    "github_reviewed": true,
+    "github_reviewed_at": "2026-03-31T05:19:17Z",
+    "nvd_published_at": "2026-03-25T17:16:56Z"
+  }
+}