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High, CVSS 8.3amended

MCP Atlassian: JIRA_PROJECTS_FILTER / CONFLUENCE_SPACES_FILTER allow forbidden-project content exfiltration (one LIVE-proven on Atlassian Cloud)

CVE-2026-77251GHSA-w66g-j6c4-hcfc

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (mcp-atlassian 0.22.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.3 · 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 · score source
EPSS
  • CVE-2026-77251: 0.27% estimated exploitation activity in the next 30 days; percentile 18.54 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary mcp-atlassian is a popular community MCP server wrapper exposing Jira / Confluence to MCP clients. Operators commonly restrict the surface to a small allowlist of projects/spaces via the JIRAPROJECTSFILTER and CONFLUENCESPACESFILTER environment variables, which the README documents as the principal mechanism for limiting attacker-controlled MCP clients (= prompt-injected LLM agents) to the operator's intended subset of the workspace. We identified three distinct sub-bugs that let attacker-controlled queries read content from forbidden projects/spaces (= projects NOT in the operator's filter) despite the filter being correctly set. The most severe is empirically reproduced on production Atlassian Cloud with real operator credentials and sentinel content in two real projects. | Sub-bug | Layer | Class | Live? | |---|---|---|---| | A1 | Jira jirasearch jql | substring-bypass | 🔴 LIVE PROVEN 2026-05-18 on real Atlassian Cloud | | A2 | Confluence confluencesearch cql |…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-w66g-j6c4-hcfc

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GHSA-w66g-j6c4-hcfc

  4. Revision 1 · created ·

    Published from ghsa record GHSA-w66g-j6c4-hcfc

Agent brief

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# Patch Next advisory brief: CVE-2026-77251

Advisory: MCP Atlassian: JIRA_PROJECTS_FILTER / CONFLUENCE_SPACES_FILTER allow forbidden-project content exfiltration (one LIVE-proven on Atlassian Cloud)
IDs: CVE-2026-77251, GHSA-w66g-j6c4-hcfc
Record: https://patchnext.com/advisories/cve-2026-77251 (revision 4, source checked 26 Oct 2026, 13:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: mcp-atlassian 0.22.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI mcp-atlassian: affected < 0.22.0; fixed in 0.22.0

## Suggested inspection (read-only)
- `python -m pip show mcp-atlassian`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on mcp-atlassian.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w66g-j6c4-hcfc (GitHub-reviewed advisory GHSA-w66g-j6c4-hcfc lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0)
- Verified: https://osv.dev/vulnerability/GHSA-w66g-j6c4-hcfc (OSV record GHSA-w66g-j6c4-hcfc lists affected ranges: PyPI mcp-atlassian >=0 <0.22.0 (fixed))

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