Vulnerability-Lookup

CVE-2026-73497 (GCVE-0-2026-73497)

Vulnerability from cvelistv5 – Published: 2026-09-14 19:50 – Updated: 2026-09-15 13:56

Title

MCP Atlassian is a Model Context Protocol (MCP): DNS-rebinding TOCTOU bypass of the SSRF fix (CVE-2026-27826): unauthenticated SSRF to cloud metadata

Summary

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). From 0.17.0 until 0.22.0, validate_url_for_ssrf resolves the attacker-controlled X-Atlassian-Jira-Url and X-Atlassian-Confluence-Url header host once at middleware time, but the outbound request is built with the raw hostname and resolves it again at connection time with no IP pinning. An attacker-controlled DNS-rebinding name can return a public IP during validation and 169.254.169.254 or another internal IP during connection, enabling unauthenticated server-side requests to cloud metadata or internal services. The flaw spans src/mcp_atlassian/utils/urls.py, src/mcp_atlassian/servers/main.py, and src/mcp_atlassian/servers/dependencies.py; validate_url_for_ssrf returns only a verdict rather than a pinned IP, UserTokenMiddleware processes the attacker-controlled headers before fetcher creation, and the Jira and Confluence fetchers use the raw hostname. This issue is fixed in version 0.22.0.

Severity

6.5 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-15 13:25 UTC

CWE

CWE-918 - Server-Side Request Forgery (SSRF)

Assigner

GitHub_M mitre root

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: >= 0.17.0, < 0.22.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-73497

Vulnerability from fkie_nvd - Published: 2026-09-14 20:16 - Updated: 2026-09-15 14:17

Severity

6.5 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460
	security-advisories@github.com	https://github.com/sooperset/mcp-atlassian/pull/1448
	security-advisories@github.com	https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0
	security-advisories@github.com	https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-489g-7rxv-6c8q

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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          "product": "mcp-atlassian",
          "vendor": "sooperset",
          "versions": [
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    }
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}

GHSA-489G-7RXV-6C8Q

Vulnerability from github – Published: 2026-07-10 18:01 – Updated: 2026-07-10 18:01

Summary

MCP Atlassian: DNS-rebinding TOCTOU bypass of the SSRF fix (CVE-2026-27826)

Details

Summary

GHSA-7r34-79r5-rcc9's fix added validate_url_for_ssrf, which resolves the attacker-controlled X-Atlassian-{Jira,Confluence}-Url header host once at middleware time and trusts the result. But the outbound request is later built with the raw hostname and re-resolves at connect time with no IP pinning. An attacker-controlled rebinding DNS name returns a public IP on the guard's lookup (validation passes) and 169.254.169.254 / an internal IP on the request's lookup (the socket connects there) → unauthenticated SSRF to cloud metadata / internal services on the patched build.

Relationship to CVE-2026-27826 / GHSA-7r34-79r5-rcc9 (incomplete fix — please read first)

This is an incomplete-fix sibling of the published GHSA-7r34-79r5-rcc9 (the X-Atlassian-*-Url header SSRF). That fix (PR #986/#1005) added a single middleware-time resolve + allowlist DNS-skip, but does not pin the validated IP to the connection — the fetcher re-resolves the raw hostname at connect time, so the documented SSRF mitigation is incomplete against DNS-rebinding. The other advisory GHSA-xjgw-4wvw-rgm4 (file-write) is unrelated. Verified live (2026-06-27): neither advisory, nor any open PR/issue (rebind/TOCTOU/getaddrinfo/pin → 0), covers connect-time re-resolution. Filing as an incomplete-fix of GHSA-7r34 (not a standalone fresh SSRF).

Affected

src/mcp_atlassian/utils/urls.py + servers/main.py + servers/dependencies.py, HEAD ba72540 (PyPI mcp-atlassian, patched ≥0.17.0). CWE-918 (SSRF) via CWE-367 (TOCTOU).

Vulnerable code

utils/urls.py validate_url_for_ssrf (≈184-205) resolves + validates, then returns a string verdict, not a pinned IP:

def validate_url_for_ssrf(url: str) -> str | None:   # returns an error string or None — NO IP is pinned
    ...
    # resolves the host, checks each resolved IP is global, then DISCARDS the IP

servers/main.py:526,534 calls it once in middleware. servers/dependencies.py:544-561 then builds the fetcher with url = <raw header hostname> (no pinned IP, no custom resolver / cached-getaddrinfo adapter), so the actual request re-resolves the name.

PoC (executed — boundary demonstration)

The PoC loads the real urls.py by path (importlib, sha256 printed) and drives the genuine validate_url_for_ssrf, simulating the two resolutions via getaddrinfo:

[CHECK ] validate_url_for_ssrf('http://rebind.attacker.example') -> None        (getaddrinfo#1 = 93.184.216.34 global -> guard PASSED)
[CONNECT] getaddrinfo call #2 returned 169.254.169.254 -> the socket connects HERE
[PROOF ] guard validated IP 93.184.216.34 but connection targets 169.254.169.254  => SSRF on the PATCHED build
[CONTROL] if guard SAW 169.254.169.254 at check time -> blocks it correctly
[PIN   ] validate_url_for_ssrf returns a verdict (None), NOT an IP; dependencies.py builds url=raw hostname -> NO pin
ALL PoC ASSERTIONS PASSED — DNS-rebind TOCTOU bypass demonstrated.

Honest scope of the PoC: this is a boundary demonstration — it proves the structural TOCTOU (the guard validates an IP it then discards; the connection re-resolves an unpinned hostname). It does not demonstrate a live end-to-end SSRF on a running server; that additionally requires an attacker-controlled fast-rebinding authoritative DNS responder winning the resolve→connect window. Flagging this explicitly rather than overclaiming.

Impact

Same as parent GHSA-7r34 (unauth read of cloud-metadata IAM creds / internal-service reach), reachable again on the patched version. The X-Atlassian-*-Url headers are processed in UserTokenMiddleware before fetcher creation, so an unauthenticated/low-priv caller controls the host.

Severity

High — CVSS v3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N ≈ 7.x, aligned to the parent (8.2) with AC:H for the rebinding-race precondition. Honest caveat (above): the executed PoC proves the missing IP-pin structurally; a live exploit additionally needs an attacker rebinding-DNS. Not Critical.

Remediation

Pin the connection to the IP that validate_url_for_ssrf validated: use a custom resolver / cached-getaddrinfo requests-adapter (or pass the validated IP with a Host header), so the connect cannot re-resolve to a different address.

Dedup / freshness (re-verified live 2026-06-27)

Advisories GHSA-7r34-79r5-rcc9 (original header SSRF this bypasses) + GHSA-xjgw-4wvw-rgm4 (file-write, unrelated). Neither covers connect-time re-resolution / rebinding. PR #986/#1005 (the fix) add a single middleware-time resolve + allowlist DNS-skip, no pinning. gh search prs/issues for rebind/TOCTOU/getaddrinfo/pin → 0. First-party code. Fresh at HEAD ba72540.

Severity

6.5 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "mcp-atlassian"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.22.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-918"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-10T18:01:22Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\nGHSA-7r34-79r5-rcc9\u0027s fix added `validate_url_for_ssrf`, which resolves the attacker-controlled `X-Atlassian-{Jira,Confluence}-Url` header host **once at middleware time** and trusts the result. But the outbound request is later built with the **raw hostname** and **re-resolves at connect time with no IP pinning**. An attacker-controlled rebinding DNS name returns a public IP on the guard\u0027s lookup (validation passes) and `169.254.169.254` / an internal IP on the request\u0027s lookup (the socket connects there) \u2192 unauthenticated SSRF to cloud metadata / internal services on the **patched** build.\n\n### Relationship to CVE-2026-27826 / GHSA-7r34-79r5-rcc9 (incomplete fix \u2014 please read first)\nThis is an **incomplete-fix sibling** of the published `GHSA-7r34-79r5-rcc9` (the `X-Atlassian-*-Url` header SSRF). That fix (PR #986/#1005) added a single middleware-time resolve + allowlist DNS-skip, but **does not pin the validated IP to the connection** \u2014 the fetcher re-resolves the raw hostname at connect time, so the documented SSRF mitigation is incomplete against DNS-rebinding. The other advisory `GHSA-xjgw-4wvw-rgm4` (file-write) is unrelated. Verified live (2026-06-27): neither advisory, nor any open PR/issue (`rebind`/`TOCTOU`/`getaddrinfo`/`pin` \u2192 0), covers connect-time re-resolution. Filing as an incomplete-fix of GHSA-7r34 (not a standalone fresh SSRF).\n\n### Affected\n`src/mcp_atlassian/utils/urls.py` + `servers/main.py` + `servers/dependencies.py`, HEAD `ba72540` (PyPI `mcp-atlassian`, patched \u22650.17.0). **CWE-918** (SSRF) via **CWE-367** (TOCTOU).\n\n### Vulnerable code\n`utils/urls.py` `validate_url_for_ssrf` (\u2248184-205) resolves + validates, then returns a **string verdict, not a pinned IP**:\n```python\ndef validate_url_for_ssrf(url: str) -\u003e str | None:   # returns an error string or None \u2014 NO IP is pinned\n    ...\n    # resolves the host, checks each resolved IP is global, then DISCARDS the IP\n```\n`servers/main.py:526,534` calls it once in middleware. `servers/dependencies.py:544-561` then builds the fetcher with `url = \u003craw header hostname\u003e` (no pinned IP, no custom resolver / cached-getaddrinfo adapter), so the actual request re-resolves the name.\n\n### PoC (executed \u2014 boundary demonstration)\nThe PoC loads the **real** `urls.py` by path (`importlib`, `sha256` printed) and drives the genuine `validate_url_for_ssrf`, simulating the two resolutions via `getaddrinfo`:\n```\n[CHECK ] validate_url_for_ssrf(\u0027http://rebind.attacker.example\u0027) -\u003e None        (getaddrinfo#1 = 93.184.216.34 global -\u003e guard PASSED)\n[CONNECT] getaddrinfo call #2 returned 169.254.169.254 -\u003e the socket connects HERE\n[PROOF ] guard validated IP 93.184.216.34 but connection targets 169.254.169.254  =\u003e SSRF on the PATCHED build\n[CONTROL] if guard SAW 169.254.169.254 at check time -\u003e blocks it correctly\n[PIN   ] validate_url_for_ssrf returns a verdict (None), NOT an IP; dependencies.py builds url=raw hostname -\u003e NO pin\nALL PoC ASSERTIONS PASSED \u2014 DNS-rebind TOCTOU bypass demonstrated.\n```\n**Honest scope of the PoC:** this is a **boundary** demonstration \u2014 it proves the structural TOCTOU (the guard validates an IP it then discards; the connection re-resolves an unpinned hostname). It does **not** demonstrate a live end-to-end SSRF on a running server; that additionally requires an attacker-controlled fast-rebinding authoritative DNS responder winning the resolve\u2192connect window. Flagging this explicitly rather than overclaiming.\n\n### Impact\nSame as parent GHSA-7r34 (unauth read of cloud-metadata IAM creds / internal-service reach), reachable again on the patched version. The `X-Atlassian-*-Url` headers are processed in `UserTokenMiddleware` before fetcher creation, so an unauthenticated/low-priv caller controls the host.\n\n### Severity\n**High \u2014 CVSS v3.1 `AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N` \u2248 7.x**, aligned to the parent (8.2) with `AC:H` for the rebinding-race precondition. Honest caveat (above): the executed PoC proves the missing IP-pin structurally; a live exploit additionally needs an attacker rebinding-DNS. Not Critical.\n\n### Remediation\nPin the connection to the IP that `validate_url_for_ssrf` validated: use a custom resolver / cached-`getaddrinfo` `requests`-adapter (or pass the validated IP with a `Host` header), so the connect cannot re-resolve to a different address.\n\n### Dedup / freshness (re-verified live 2026-06-27)\nAdvisories `GHSA-7r34-79r5-rcc9` (original header SSRF this bypasses) + `GHSA-xjgw-4wvw-rgm4` (file-write, unrelated). Neither covers connect-time re-resolution / rebinding. PR [#986](https://github.com/sooperset/mcp-atlassian/pull/986)/[#1005](https://github.com/sooperset/mcp-atlassian/pull/1005) (the fix) add a single middleware-time resolve + allowlist DNS-skip, no pinning. `gh search prs/issues` for rebind/TOCTOU/getaddrinfo/pin \u2192 0. First-party code. **Fresh** at HEAD `ba72540`.",
  "id": "GHSA-489g-7rxv-6c8q",
  "modified": "2026-07-10T18:01:22Z",
  "published": "2026-07-10T18:01:22Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-489g-7rxv-6c8q"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sooperset/mcp-atlassian"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "MCP Atlassian: DNS-rebinding TOCTOU bypass of the SSRF fix (CVE-2026-27826)"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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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.

Detection rules are retrieved from Rulezet.

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.

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.

Action not permitted

CVE-2026-73497 (GCVE-0-2026-73497)

FKIE_CVE-2026-73497

GHSA-489G-7RXV-6C8Q

Summary

Relationship to CVE-2026-27826 / GHSA-7r34-79r5-rcc9 (incomplete fix — please read first)

Affected

Vulnerable code

PoC (executed — boundary demonstration)

Impact

Severity

Remediation

Dedup / freshness (re-verified live 2026-06-27)

Tags

Sightings

Nomenclature

Related by attack behaviour