Reference page — cumulative record through Saturday, October 3, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-77255

CVE-2026-77255HIGH

sooperset mcp-atlassian — MCP Atlassian: Arbitrary File Read & Exfiltration (Confused Deputy) in JIRA update_issue

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   L   N   N  C  H  N  N    8.6   .0041   32.7     —

AFFECTED
  Product        Versions    Fixed
  mcp-atlassian  < 0.22.0 –  —

TIMELINE
  Aug 20  Reserved by GitHub_M
  Sep 22  Published (CNA: GitHub_M)
  Sep 29  EXPLOIT PUBLISHED — CVE-2026-77255 (sooperset mcp-atlassian). Public exploit reference added.

CWE-22, CWE-441 · CNA: GitHub_M · CVSS v3.1 · 4 references · NVD status: Analyzed

Description

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the Jira update_issue attachments argument is converted into local paths and routed to the attachment upload implementation without workspace validation. A caller can make the MCP server read arbitrary local files and attach them to a Jira issue, using the server as a confused deputy to exfiltrate the contents. The advisory traces the vulnerable input and processing flow through jira update_issue, attachments, upload_attachment, and file_path, which identify the affected entry points, controls, and code paths. This issue is fixed in version 0.22.0.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
August 20, 2026	Reserved	Reserved by GitHub_M
September 22, 2026	Published	Published (CNA: GitHub_M)
September 29, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-77255 (sooperset mcp-atlassian). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
sooperset	mcp-atlassian	—	< 0.22.0	—

Weaknesses

CWE-22 · CWE-441

References (4)

https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460 [Patch]
https://github.com/sooperset/mcp-atlassian/pull/1448 [Issue Tracking, Patch]
https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0 [Release Notes]
https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-2xj6-xx86-cwwc [Exploit, Vendor Advisory]

Authoritative record: CVE-2026-77255 at cve.org

Vendors: sooperset

Weaknesses: CWE-22 · CWE-441

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-77255 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Saturday, October 3, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.