Vulnerability-Lookup

CVE-2026-77250 (GCVE-0-2026-77250)

Vulnerability from cvelistv5 – Published: 2026-09-22 17:51 – Updated: 2026-09-22 18:42

Title

MCP Atlassian: OAuth fallback token storage writes plaintext access and refresh tokens with group-readable permissions

Summary

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, OAuthConfig writes a plaintext fallback file containing access and refresh tokens under the user's .mcp-atlassian directory using process-default permissions. On systems with a permissive umask, same-group or other local users and processes can read the persisted tokens and reuse the associated Atlassian access. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens, ~/.mcp-atlassian/oauth-<client_id>.json, access_token, and refresh_token, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

Severity

6.1 (Medium)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-22 18:42 UTC

CWE

CWE-312 - Cleartext Storage of Sensitive Information

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/sooperset/mcp-atlassian/securi…	x_refsource_CONFIRM
https://github.com/sooperset/mcp-atlassian/pull/1448	x_refsource_MISC
https://github.com/sooperset/mcp-atlassian/commit…	x_refsource_MISC
https://github.com/sooperset/mcp-atlassian/releas…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
sooperset	mcp-atlassian	Affected: < 0.22.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-77250

Vulnerability from fkie_nvd - Published: 2026-09-22 18:17 - Updated: 2026-09-23 18:28

Severity

6.1 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460
	security-advisories@github.com	https://github.com/sooperset/mcp-atlassian/pull/1448
	security-advisories@github.com	https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0
	security-advisories@github.com	https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-g5xv-mhgm-v5f6
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-g5xv-mhgm-v5f6

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "mcp-atlassian",
          "vendor": "sooperset",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.22.0"
            }
          ]
        }
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      "source": "security-advisories@github.com"
    }
  ],
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  "descriptions": [
    {
      "lang": "en",
      "value": "MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, OAuthConfig writes a plaintext fallback file containing access and refresh tokens under the user\u0027s .mcp-atlassian directory using process-default permissions. On systems with a permissive umask, same-group or other local users and processes can read the persisted tokens and reuse the associated Atlassian access. The advisory traces the vulnerable input and processing flow through OAuthConfig._save_tokens, ~/.mcp-atlassian/oauth-\u003cclient_id\u003e.json, access_token, and refresh_token, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0."
    }
  ],
  "id": "CVE-2026-77250",
  "lastModified": "2026-09-23T18:28:25.093",
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      "type": "Secondary"
    }
  ]
}

GHSA-G5XV-MHGM-V5F6

Vulnerability from github – Published: 2026-09-22 20:36 – Updated: 2026-09-22 20:36

Summary

MCP Atlassian: OAuth fallback token storage writes plaintext access and refresh tokens with group-readable permissions

Details

Summary

When OAuth tokens are saved, MCP Atlassian always writes a plaintext fallback copy under ~/.mcp-atlassian/oauth-<client_id>.json. The fallback file is created with the process default umask rather than restrictive permissions. In this environment the file was created as mode 0664, exposing access and refresh tokens to same-group local users and any process that can read the home directory.

Details

OAuthConfig._save_tokens() stores OAuth token data in keyring, but it also unconditionally maintains a plaintext file fallback for backwards compatibility in src/mcp_atlassian/utils/oauth.py:350-386. If keyring saving fails it also falls back to the same file path in src/mcp_atlassian/utils/oauth.py:387-391.

The fallback writer creates ~/.mcp-atlassian and then writes oauth-<client_id>.json with a normal open(token_path, "w") call in src/mcp_atlassian/utils/oauth.py:392-420. No mode=0o600, os.open(..., 0o600), chmod, or owner-only directory permission is applied. The file contains both access_token and refresh_token (src/mcp_atlassian/utils/oauth.py:360-367) and is later loaded from the same plaintext path in src/mcp_atlassian/utils/oauth.py:450-470.

The security policy warns that OAuth client credentials and secrets should not be exposed (SECURITY.md:39-44), but the current implementation creates a persistent plaintext token copy even when keyring succeeds.

PoC

The following safe local proof uses a temporary HOME and mocked keyring writes. It creates and deletes only temporary files.

uv run python - <<'PY'
import json, os, shutil, stat, tempfile
from pathlib import Path
from unittest.mock import patch
from mcp_atlassian.utils.oauth import OAuthConfig

home = tempfile.mkdtemp(prefix='mcp-atlassian-oauth-poc-')
old_home = os.environ.get('HOME')
os.environ['HOME'] = home
try:
    cfg = OAuthConfig(client_id='poc-client', client_secret='client-secret', redirect_uri='http://localhost/callback', scope='offline_access', cloud_id='cloud-id')
    cfg.access_token = 'poc-access-token'
    cfg.refresh_token = 'poc-refresh-token'
    cfg.expires_at = 2000000000
    with patch('keyring.set_password', return_value=None):
        cfg._save_tokens()
    token_file = Path(home) / '.mcp-atlassian' / 'oauth-poc-client.json'
    mode = stat.S_IMODE(token_file.stat().st_mode)
    data = json.loads(token_file.read_text())
    print(json.dumps({
        'token_file_exists': token_file.exists(),
        'token_file_mode_octal': oct(mode),
        'contains_access_token': data.get('access_token') == 'poc-access-token',
        'contains_refresh_token': data.get('refresh_token') == 'poc-refresh-token',
        'token_file_path': str(token_file),
    }, indent=2, sort_keys=True))
finally:
    if old_home is not None:
        os.environ['HOME'] = old_home
    else:
        os.environ.pop('HOME', None)
    shutil.rmtree(home)
PY

Observed output from this environment:

{
  "contains_access_token": true,
  "contains_refresh_token": true,
  "token_file_exists": true,
  "token_file_mode_octal": "0o664",
  "token_file_path": "/tmp/mcp-atlassian-oauth-poc-9m9wvktp/.mcp-atlassian/oauth-poc-client.json"
}

The proof confirms that a plaintext file containing both access and refresh tokens is created and is not owner-only.

Impact

A local user, container sidecar, compromised dependency, backup job, or other process with filesystem read access to the account's home directory can recover OAuth access and refresh tokens. Refresh tokens can allow continued Atlassian API access until revoked or expired, depending on the OAuth app and token policy. In shared hosts, Kubernetes volumes, developer workstations, and CI runners, this can lead to persistent Atlassian account compromise.

Severity

6.1 (Medium)


                  
                    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "mcp-atlassian"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.22.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-77250"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-312"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-22T20:36:34Z",
    "nvd_published_at": "2026-09-22T18:17:17Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nWhen OAuth tokens are saved, MCP Atlassian always writes a plaintext fallback copy under `~/.mcp-atlassian/oauth-\u003cclient_id\u003e.json`. The fallback file is created with the process default umask rather than restrictive permissions. In this environment the file was created as mode `0664`, exposing access and refresh tokens to same-group local users and any process that can read the home directory.\n\n### Details\n\n`OAuthConfig._save_tokens()` stores OAuth token data in keyring, but it also unconditionally maintains a plaintext file fallback for backwards compatibility in `src/mcp_atlassian/utils/oauth.py:350-386`. If keyring saving fails it also falls back to the same file path in `src/mcp_atlassian/utils/oauth.py:387-391`.\n\nThe fallback writer creates `~/.mcp-atlassian` and then writes `oauth-\u003cclient_id\u003e.json` with a normal `open(token_path, \"w\")` call in `src/mcp_atlassian/utils/oauth.py:392-420`. No `mode=0o600`, `os.open(..., 0o600)`, `chmod`, or owner-only directory permission is applied. The file contains both `access_token` and `refresh_token` (`src/mcp_atlassian/utils/oauth.py:360-367`) and is later loaded from the same plaintext path in `src/mcp_atlassian/utils/oauth.py:450-470`.\n\nThe security policy warns that OAuth client credentials and secrets should not be exposed (`SECURITY.md:39-44`), but the current implementation creates a persistent plaintext token copy even when keyring succeeds.\n\n### PoC\n\nThe following safe local proof uses a temporary `HOME` and mocked keyring writes. It creates and deletes only temporary files.\n\n```bash\nuv run python - \u003c\u003c\u0027PY\u0027\nimport json, os, shutil, stat, tempfile\nfrom pathlib import Path\nfrom unittest.mock import patch\nfrom mcp_atlassian.utils.oauth import OAuthConfig\n\nhome = tempfile.mkdtemp(prefix=\u0027mcp-atlassian-oauth-poc-\u0027)\nold_home = os.environ.get(\u0027HOME\u0027)\nos.environ[\u0027HOME\u0027] = home\ntry:\n    cfg = OAuthConfig(client_id=\u0027poc-client\u0027, client_secret=\u0027client-secret\u0027, redirect_uri=\u0027http://localhost/callback\u0027, scope=\u0027offline_access\u0027, cloud_id=\u0027cloud-id\u0027)\n    cfg.access_token = \u0027poc-access-token\u0027\n    cfg.refresh_token = \u0027poc-refresh-token\u0027\n    cfg.expires_at = 2000000000\n    with patch(\u0027keyring.set_password\u0027, return_value=None):\n        cfg._save_tokens()\n    token_file = Path(home) / \u0027.mcp-atlassian\u0027 / \u0027oauth-poc-client.json\u0027\n    mode = stat.S_IMODE(token_file.stat().st_mode)\n    data = json.loads(token_file.read_text())\n    print(json.dumps({\n        \u0027token_file_exists\u0027: token_file.exists(),\n        \u0027token_file_mode_octal\u0027: oct(mode),\n        \u0027contains_access_token\u0027: data.get(\u0027access_token\u0027) == \u0027poc-access-token\u0027,\n        \u0027contains_refresh_token\u0027: data.get(\u0027refresh_token\u0027) == \u0027poc-refresh-token\u0027,\n        \u0027token_file_path\u0027: str(token_file),\n    }, indent=2, sort_keys=True))\nfinally:\n    if old_home is not None:\n        os.environ[\u0027HOME\u0027] = old_home\n    else:\n        os.environ.pop(\u0027HOME\u0027, None)\n    shutil.rmtree(home)\nPY\n```\n\nObserved output from this environment:\n\n```json\n{\n  \"contains_access_token\": true,\n  \"contains_refresh_token\": true,\n  \"token_file_exists\": true,\n  \"token_file_mode_octal\": \"0o664\",\n  \"token_file_path\": \"/tmp/mcp-atlassian-oauth-poc-9m9wvktp/.mcp-atlassian/oauth-poc-client.json\"\n}\n```\n\nThe proof confirms that a plaintext file containing both access and refresh tokens is created and is not owner-only.\n\n### Impact\n\nA local user, container sidecar, compromised dependency, backup job, or other process with filesystem read access to the account\u0027s home directory can recover OAuth access and refresh tokens. Refresh tokens can allow continued Atlassian API access until revoked or expired, depending on the OAuth app and token policy. In shared hosts, Kubernetes volumes, developer workstations, and CI runners, this can lead to persistent Atlassian account compromise.",
  "id": "GHSA-g5xv-mhgm-v5f6",
  "modified": "2026-09-22T20:36:34Z",
  "published": "2026-09-22T20:36:34Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-g5xv-mhgm-v5f6"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-77250"
    },
    {
      "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "MCP Atlassian: OAuth fallback token storage writes plaintext access and refresh tokens with group-readable permissions"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
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Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Action not permitted

CVE-2026-77250 (GCVE-0-2026-77250)

FKIE_CVE-2026-77250

GHSA-G5XV-MHGM-V5F6

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Details

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