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PatchSiren cyber security CVE debrief

CVE-2026-77248 sooperset CVE debrief

An unauthenticated network caller can read files available to the MCP process, upload them to an attacker-selected Jira issue or Confluence page, and retrieve the contents due to vulnerabilities in MCP Atlassian versions prior to 0.22.0. This issue allows for potential data exfiltration or unauthorized file uploads, compromising the integrity of the MCP process. Defenders should assess exposure and prioritize upgrading to version 0.22.0 or later, especially for installations with publicly accessible streamable HTTP transport.

Vendor
sooperset
Product
mcp-atlassian
CVSS
HIGH 8.6
CISA KEV
Not listed in stored evidence
Original CVE published
2026-09-22
Original CVE updated
2026-09-28
Advisory published
2026-09-22
Advisory updated
2026-09-28

Who should care

Defenders of MCP Atlassian installations, especially those with publicly accessible streamable HTTP transport, should assess exposure and prioritize upgrading to version 0.22.0 or later.

Why it matters

CVE-2026-77248 allows unauthenticated network callers to read and upload files, potentially leading to data exfiltration or MCP process compromise, requiring defenders to verify exposure and prioritize upgrades.

  • Unauthenticated file access and retrieval
  • Potential data exfiltration or unauthorized file uploads
  • Compromise of MCP process integrity
  • Verification of MCP Atlassian installations for exposure

Technical summary

MCP Atlassian versions prior to 0.22.0 have vulnerabilities in streamable HTTP transport and upload_attachment, allowing unauthenticated network callers to read files, upload them to Jira issues or Confluence pages, and retrieve contents. The advisory traces the vulnerable input and processing flow through streamable-http, UserTokenMiddleware, upload_attachment, file_path, and _get_fetcher, identifying affected entry points, controls, and code paths. This issue is fixed in version 0.22.0, which addresses the vulnerabilities and prevents unauthorized access and file uploads.

Defensive priority

Defenders should prioritize verifying exposure of MCP Atlassian installations, especially those with publicly accessible streamable HTTP transport, and upgrade to version 0.22.0 or later.

Recommended defensive actions

  • Verify MCP Atlassian installations for exposure, especially those with publicly accessible streamable HTTP transport
  • Upgrade to version 0.22.0 or later
  • Restrict access to streamable HTTP transport
  • Monitor for suspicious file uploads and retrievals
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The advisory traces the vulnerable input and processing flow through streamable-http, UserTokenMiddleware, upload_attachment, file_path, and _get_fetcher, identifying affected entry points, controls, and code paths.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-77248 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-77248

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-77248 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-77248

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.