Summary
MCP Atlassian: ENABLED_TOOLS / Toolset authorization bypass
ENABLED_TOOLS and TOOLSETS filters are enforced at tools/list time only. tools/call dispatches from the full unfiltered tool registry (73 tools). Any user with access to the server endpoint that knows a tool name can invoke it directly. Tool names are not secret since mcp-atlassian is open source. Any direct JSON-RPC call bypasses the restriction entirely.
READ_ONLY_MODE is not affected: it has dual enforcement at list time (_list_tools_mcp) and call time @check_write_access decorator. The developers applied the correct pattern to READ_ONLY_MODE but not to ENABLED_TOOLS or toolsets - confirming this is an implementation oversight.
Details
In src/mcp_atlassian/servers/main.py, AtlassianMCP overrides _list_tools_mcp and applies the TOOLSETS and ENABLED_TOOLS filters before returning the tool list to clients. The _call_tool_mcp handler is not overridden. FastMCP's default _call_tool_mcp resolves the tool from the local tool manager / mounted servers, the full unfiltered inventory, so the filters never apply at call time.
Proof of Concept
All calls are issued against the HTTP transport, with ENABLED_TOOLS=jira_search configured - only jira_search should be reachable.
Step 1 - negative control: tools/list correctly filters by ENABLED_TOOLS:
req → tools/list
← { "tools": [ { "name": "jira_search" } ] } # only 1 tool; jira_get_issue / jira_create_issue absent
Step 2 - confidentiality bypass: tools/call dispatches jira_get_issue despite its exclusion from the list:
req → tools/call jira_get_issue { "issue_key": "SEC-1" }
← { ... issue fields (summary, status, ...) ... } # executed; not blocked
Step 3 - integrity bypass: tools/call dispatches the write tool jira_create_issue:
req → tools/call jira_create_issue
{ "project_key": "SEC", "summary": "[PoC] ENABLED_TOOLS bypass", "issue_type": "Task" }
← { ... "key": "SEC-<n>" ... } # issue created despite ENABLED_TOOLS=jira_search
Step 1 proves the filter exists and is enforced at list time, so Steps 2–3 are a genuine authorization bypass, not an open/unconfigured endpoint. The same result holds with TOOLSETS=jira_read configured: write tools are absent from tools/list yet execute via tools/call.
Local reproduction
Extract enabled_tools_bypass_tool_authorization.zip:
# Fill Atlassian credentials in docker-compose.yml (ENABLED_TOOLS=jira_search is preset);
# ensure issue SEC-1 exists, or update the project/issue key in poc.sh
docker compose up -d # mcp-atlassian, streamable-http, 0.0.0.0, ENABLED_TOOLS=jira_search
./poc.sh # exits 0 on success
docker compose down -v
Requires Docker, curl, jq, and an Atlassian Cloud site with a Jira project (free tier works). The script runs the three steps above: it confirms tools/list returns only jira_search, then dispatches the excluded jira_get_issue (read) and jira_create_issue (write) via tools/call. The test issue it creates is deleted automatically on exit.
Credit
Discovered by Francisco Rosales of Manifold Security
Impact
Any user with access to the MCP server's HTTP endpoint can invoke any of the 73 registered tools regardless of ENABLED_TOOLS or TOOLSETS configuration - including write and delete operations on Jira issues, Confluence pages, etc. Operators deploying mcp-atlassian via Streamable HTTP rely on ENABLED_TOOLS to enforce least-privilege access; the bypass invalidates that model entirely.
The security impact concentrates in multi-user / HTTP-transport deployments, where the tool filter is a trust boundary between clients. In a single-user stdio deployment there is no second principal to defend against.
The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.
CVE-2026-77243 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.22.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-77243? CVE-2026-77243 is a high-severity missing authorization vulnerability in mcp-atlassian (pip), affecting versions < 0.22.0. It is fixed in 0.22.0. The application does not perform an authorization check before performing a sensitive operation.
- How severe is CVE-2026-77243? CVE-2026-77243 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of mcp-atlassian are affected by CVE-2026-77243? mcp-atlassian (pip) versions < 0.22.0 is affected.
- Is there a fix for CVE-2026-77243? Yes. CVE-2026-77243 is fixed in 0.22.0. Upgrade to this version or later.
- Is CVE-2026-77243 exploitable, and should I be worried? Whether CVE-2026-77243 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-77243 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-77243? Upgrade
mcp-atlassianto 0.22.0 or later.