CVE-2026-77244: [mcp-atlassian] Authentication bypass in HTTP transport: AtlassianOpaqueTokenVerifier accepts any non-empty token

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.3%, percentile 20: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 20% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes mcp-atlassian (PyPI) < 0.22.0, fixed in 0.22.0. Check your lockfile, including transitive dependencies.

What it is

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the HTTP transport accepts requests without a verified user identity and downstream fetcher construction falls back to the operator's globally configured Jira or Confluence credentials. A network client that can reach the MCP endpoint can invoke Atlassian tools as the operator, including read and write operations available to that account. The advisory traces the vulnerable input and processing flow through UserTokenMiddleware, AtlassianOpaqueTokenVerifier, getfetcher, and streamable-http, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

From the GitHub advisory

Description

mcp-atlassian deploys in two common patterns:

Pattern A (single-user, server-side credentials): operator sets JIRAUSERNAME + JIRAAPITOKEN (or CONFLUENCEUSERNAME + CONFLUENCEAPITOKEN) in environment variables. Server uses these to call Jira/Confluence. This is the documented quickstart pattern.

Pattern B (multi-user, OAuth or per-request PAT): operator sets up OAuth proxy or accepts per-user tokens via Authorization or service headers.

The authentication mechanism in HTTP transport has two issues that combine to permit unauthenticated access to Pattern A deployments:

Weakness type: CWE-287, CWE-303, CWE-862.

Product: mcp-atlassian (PyPI) · Assigned by: GitHub_M · Published: 2026-09-22

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.29% probability of exploitation activity in the next 30 days; percentile 20.

Timeline

• 2026-09-22 — CVE record published by GitHub_M
• 2026-09-22 — GitHub-reviewed advisory GHSA-wrhw-j3f9-8vc6 published (critical)
• 2026-09-23 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-wrhw-j3f9-8vc6 github.com
2. CVE.org record CVE-2026-77244 cve.org
3. NVD entry CVE-2026-77244 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

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