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MCP Atlassian: OAuth refresh-token backup file is world-readable under default Unix umask

Type: advisorySources: OSV

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the plaintext OAuth fallback file containing refresh and access tokens is written with permissions inherited from the process umask. Under common or permissive configurations, other local users can read the backup and retain Atlassian access through the refresh token. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens_to_file, refresh_token, access_token, and umask, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-77256
Confirmed fixed CVEs
Not specified
Updated in this feed
7 Nov 2026, 16:21 UTC · Revision 1

Source evidence

MCP Atlassian: OAuth refresh-token backup file is world-readable under default Unix umask

core-osv · Original source

Published 22 Sept 2026, 18:48 UTC

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the plaintext OAuth fallback file containing refresh and access tokens is written with permissions inherited from the process umask. Under common or permissive configurations, other local users can read the backup and retain Atlassian access through the refresh token. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens_to_file, refresh_token, access_token, and umask, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

osv:CVE-2026-77256
Complete source record
{
  "id": "f1eb155876237a293a108ccf242f17897dd23e818a7220b913ed8a91214c3534",
  "url": "https://osv.dev/vulnerability/CVE-2026-77256",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "MCP Atlassian: OAuth refresh-token backup file is world-readable under default Unix umask",
    "summary": "MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the plaintext OAuth fallback file containing refresh and access tokens is written with permissions inherited from the process umask. Under common or permissive configurations, other local users can read the backup and retain Atlassian access through the refresh token. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens_to_file, refresh_token, access_token, and umask, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.",
    "evidence": "osv:CVE-2026-77256",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-77256",
      "aliases": [
        "CVE-2026-77256",
        "GHSA-76pr-5669-3xf5"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/sooperset/mcp-atlassian",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "b041733473f95119dd539542a43c280737a8e460"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "0.22.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "b041733473f95119dd539542a43c280737a8e460"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "b041733473f95119dd539542a43c280737a8e460"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v0.22.0"
                  },
                  {
                    "cpe": "cpe:2.3:a:mcp-atlassian:mcp_atlassian:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "0.22.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v0.21.1",
            "v0.21.0",
            "v0.20.1",
            "v0.20.0",
            "v0.19.0",
            "v0.18.1",
            "v0.18.0",
            "v0.17.0",
            "v0.16.1",
            "v0.16.0",
            "v0.15.0",
            "v0.14.3",
            "v0.14.2",
            "v0.14.1",
            "v0.14.0",
            "v0.13.1",
            "v0.13.0",
            "v0.12.0",
            "v0.11.12",
            "v0.11.11",
            "v0.11.10",
            "v0.11.9",
            "v0.11.8",
            "v0.11.7",
            "v0.11.6",
            "v0.11.5",
            "v0.11.4",
            "v0.11.3",
            "v0.11.2",
            "v0.11.1",
            "v0.11.0",
            "v0.10.6",
            "v0.10.5",
            "v0.10.4",
            "v0.10.3",
            "v0.10.2",
            "v0.10.1",
            "v0.10.0",
            "v0.9.0",
            "v0.8.4",
            "v0.8.3",
            "v0.8.2",
            "v0.8.1",
            "v0.8.0",
            "v0.7.1",
            "v0.7.0",
            "v0.6.5",
            "v0.6.4",
            "v0.6.3",
            "v0.6.2",
            "v0.6.1",
            "v0.6.0",
            "v0.5.0",
            "v0.4.0",
            "v0.3.1",
            "v0.3.0",
            "v0.2.6",
            "v0.2.5",
            "v0.2.4",
            "v0.2.3",
            "v0.2.2",
            "v0.2.1",
            "v0.2.0",
            "v0.1.16",
            "v0.1.15",
            "v0.1.14",
            "v0.1.13",
            "v0.1.12",
            "v0.1.11",
            "v0.1.10",
            "v0.1.8",
            "v0.1.7",
            "v0.1.6",
            "v0.1.5",
            "v0.1.4"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-77256.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:51.223360983Z",
      "provider": "osv",
      "references": [
        "https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/77xxx/CVE-2026-77256.json",
        "https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-76pr-5669-3xf5",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-77256",
        "https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460",
        "https://github.com/sooperset/mcp-atlassian/pull/1448"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-732"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/77xxx/CVE-2026-77256.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-77256",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 519862,
  "published_at": "2026-09-22T18:48:58.48+00:00"
}