Vulnerability in mcp-atlassian (CVE-2026-77250)
Summary
Vulnerability in mcp-atlassian (CVE-2026-77250). Confidential information can be exposed externally. Exploitable via chmod. Mitigation: upgrade to 0.22.0 or later.
Original description
The description as published by the source.
Summary
When OAuth tokens are saved, MCP Atlassian always writes a plaintext fallback copy under ~/.mcp-atlassian/oauth-.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-.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. I…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-77250 has been found in mcp-atlassian.
Attackers can target a specific entry point like chmod over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 6.1/10.
What to do: upgrade mcp-atlassian to 0.22.0 or later.
If unsure, ask your IT team or search "mcp-atlassian CVE-2026-77250" on the vendor's site.
CVE-2026-77250 (mcp-atlassian) — CWE-312 / CVSS v3 6.1
Attack vector: local / no user interaction
Attack surface: chmod / access_token / refresh_token / HOME
Patched: 0.22.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-312) exists in mcp-atlassian. Attackers reach the vulnerable code path via chmod.
Check the vendor advisory for the affected versions of mcp-atlassian. Attack surface: chmod / access_token / refresh_token / HOME.
Severity: Medium (CVSS 6.1/10). Confidential information can be exposed externally.
Update to 0.22.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'mcp-atlassian' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'mcp-atlassian' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
mcp-atlassianを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade mcp-atlassian to 0.22.0ステージング環境で 0.22.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com
- web github.com