The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.27.2, the SSE and stateful Streamable HTTP transports mcp.server.sse.SseServerTransport and mcp.server.streamable_http_manager.StreamableHTTPSessionManager route requests to existing sessions using only the session_id query parameter or Mcp-Session-Id header without verifying the authenticated principal that created the session, allowing a different bearer-token-authenticated client with a known session ID to inject JSON-RPC messages into that session. This issue is fixed in version 1.27.2.
CVE-2026-52869
HIGHPre-NVD 7.17.1—
EchelonGraph scoreMEDIUM confidence
This high-severity CVE scores 7.1 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 84% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: epss, secondary
7.1
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 7.1Exploit: NoneExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 7.1
- EG Score
- 7.1(medium)
- EG Risk
- 32(Track)EG Risk 32/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity71% × 45%Exploitation0% × 40%Automatability0% × 15%Action: Routine — remediate on your standard cadence. - EPSS
- 16.4%
- KEV
- Not listed
Published
July 15, 2026
Last Modified
July 17, 2026
Advisory Details (6)
Auto-updated Jul 15, 2026Patch available. Sources: github_commit, github_pr, github_release, github.
github Patch Available
HTTP transports serve session requests without verifying the authenticated principal · Advisory · modelcontextprotocol/python-sdk · GitHub
https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-jpw9-pfvf-9f58github_release Patch Available
v1.27.2
Patch available: modelcontextprotocol/python-sdk v1.27.2
https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.27.2github_pr Patch Available
[v1.x] Bind transport sessions to the authenticated principal
Patch available: modelcontextprotocol/python-sdk v1.27.2 (PR #2719 merged 2026-05-29)
https://github.com/modelcontextprotocol/python-sdk/pull/2719github_pr Patch Available
[v1.x] Add subject and claims to AccessToken
Patch available: modelcontextprotocol/python-sdk v1.27.2 (PR #2690 merged 2026-05-26)
https://github.com/modelcontextprotocol/python-sdk/pull/2690github_commit Patch Available
commit ce267b6fc515 (modelcontextprotocol/python-sdk)
Patch available: modelcontextprotocol/python-sdk v1.27.2 (contains commit ce267b6fc515)
https://github.com/modelcontextprotocol/python-sdk/commit/ce267b6fc515dc4efc1dc70b6975b16ff0feef0agithub_commit Patch Available
commit 1abcca2408a6 (modelcontextprotocol/python-sdk)
Patch available: modelcontextprotocol/python-sdk v1.27.2 (contains commit 1abcca2408a6)
https://github.com/modelcontextprotocol/python-sdk/commit/1abcca2408a6b50e10ec601181f63f9978705c00Vendor Advisories for CVE-2026-52869(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Affected Packages
(1 across 1 ecosystem)
PyPI(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| mcp | 0.9.1 ... 1.9.4 (55 versions) | 1.27.2 | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 10× in last 7d / 12× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-23 03:19 UTCEG score recompute
- 2026-07-22 14:08 UTCEPSS rescore
- 2026-07-21 15:25 UTCEPSS rescore
- 2026-07-20 17:08 UTCEPSS rescore
- 2026-07-19 14:31 UTCEPSS rescore
- 2026-07-19 14:31 UTCEPSS rescore
- 2026-07-19 02:37 UTCEG score recompute
- 2026-07-19 02:29 UTCEPSS rescore
- 2026-07-18 10:04 UTCEPSS rescore
- 2026-07-16 17:03 UTCEPSS rescore
- 2026-07-15 20:10 UTCEG score recompute
- 2026-07-15 20:09 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Same CWE
10 shownCWE-639
- CVE-2018-25270EG 9.8CRITICAL
- CVE-2017-20223EG 9.8CRITICAL
- CVE-2019-25487EG 9.8EPSS 94%CRITICAL
- CVE-2019-25235EG 9.8CRITICAL
- CVE-2020-16088EG 9.8CRITICAL
- CVE-2019-15310EG 9.8EPSS 94%CRITICAL
- CVE-2020-11658EG 9.8CRITICAL
- CVE-2019-15913EG 9.8CRITICAL
- CVE-2019-16340EG 9.8EPSS 97%CRITICAL
- CVE-2019-13360EG 9.8EPSS 98%CRITICAL
Frequently asked(5)
What is CVE-2026-52869?
CVE-2026-52869 is a high vulnerability published on July 15, 2026. The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). Prior to 1.27.2, the SSE and stateful Streamable HTTP transports mcp.server.sse.SseServerTransport and mcp.server.streamablehttpmanager.StreamableHTTPSessionManager route requests to existing…
When was CVE-2026-52869 disclosed?
CVE-2026-52869 was first published in the National Vulnerability Database on July 15, 2026, with the most recent update on July 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-52869 actively exploited?
CVE-2026-52869 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 16.4% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-52869?
CVE-2026-52869 has a CVSS v3 base score of 7.1 (NVD).
How do I remediate CVE-2026-52869?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-52869, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-52869
Is Your Infrastructure Affected by CVE-2026-52869?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.