CVE-2026-27826
📋 TL;DR
CVE-2026-27826 allows unauthenticated attackers to force the MCP Atlassian server to make arbitrary outbound HTTP requests by sending two custom HTTP headers without authentication. This affects all deployments of mcp-atlassian before version 0.17.0, enabling server-side request forgery (SSRF) attacks. The vulnerability resides in the HTTP middleware layer, making it invisible to tool-level code analysis.
💻 Affected Systems
- mcp-atlassian
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
In cloud deployments, attackers could steal IAM role credentials via instance metadata endpoints, potentially leading to full cloud environment compromise and data exfiltration.
Likely Case
Internal network reconnaissance, injection of attacker-controlled content into LLM tool results, and potential data leakage from internal services.
If Mitigated
Limited to denial of service through resource exhaustion if network egress is properly restricted and metadata endpoints are blocked.
🎯 Exploit Status
Exploitation requires only HTTP access to the mcp-atlassian endpoint and sending two custom headers. No authentication or special tools needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.17.0
Vendor Advisory: https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-7r34-79r5-rcc9
Restart Required: Yes
Instructions:
1. Update mcp-atlassian to version 0.17.0 or later using package manager. 2. Restart the mcp-atlassian service. 3. Verify the fix by checking the version and testing the vulnerability.
🔧 Temporary Workarounds
Network Access Restriction
linuxRestrict network access to the mcp-atlassian HTTP endpoint using firewall rules or network policies.
iptables -A INPUT -p tcp --dport [MCP_PORT] -s [TRUSTED_IPS] -j ACCEPT
iptables -A INPUT -p tcp --dport [MCP_PORT] -j DROP
Reverse Proxy Authentication
allPlace mcp-atlassian behind a reverse proxy that requires authentication before forwarding requests.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate mcp-atlassian from sensitive internal services and cloud metadata endpoints.
- Deploy web application firewall (WAF) rules to block requests containing the specific custom HTTP headers used in exploitation.
🔍 How to Verify
Check if Vulnerable:
Send an HTTP request to the mcp-atlassian endpoint with two custom headers (X-Forwarded-Host and X-Forwarded-Proto) and observe if the server makes an outbound request to a controlled URL.Check Version:
mcp-atlassian --version or check package manager (npm list mcp-atlassian)Verify Fix Applied:
After updating to 0.17.0, repeat the vulnerability test - the server should reject requests with the custom headers when no Authorization header is present.📡 Detection & Monitoring
Log Indicators:
- HTTP requests to mcp-atlassian endpoint with X-Forwarded-Host and X-Forwarded-Proto headers
- Unusual outbound HTTP requests from the mcp-atlassian process to internal or external IPs
Network Indicators:
- HTTP traffic from mcp-atlassian server to unexpected destinations, particularly cloud metadata endpoints (169.254.169.254)
- Unusual request patterns to the mcp-atlassian endpoint
SIEM Query:
source="mcp-atlassian" AND (http.headers:X-Forwarded-Host OR http.headers:X-Forwarded-Proto) AND NOT http.headers:Authorization