CVE-2026-53965

MEDIUMPre-NVD 6.96.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.9 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 70% 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
Elevated
6.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.9Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

The MCP PHP SDK (Composer package mcp/sdk) is the official Model Context Protocol SDK for PHP. In versions 0.5.0 through 0.7.0, the HTTP client transport reads a Server-Sent Events response stream incrementally and appends each chunk to an in-memory buffer with no upper bound. The buffer is only flushed when an SSE event delimiter, a double newline, is found, so a remote MCP server that streams response bytes without ever sending the delimiter causes the buffer to grow without limit. A malicious, compromised, or man-in-the-middle-controlled server that the client connects to over the HTTP transport can exploit this to exhaust the client process's memory, triggering a fatal allocation error or OS out-of-memory kill and denying service to the MCP client. The issue affects any client using HttpTransport against an untrusted server endpoint and does not require authentication or user interaction beyond initiating the connection. This issue is fixed in version 0.7.1.

CVSS v3
6.9
EG Score
6.9(medium)
EG Risk
47(Track)
EG Risk 47/100SSVC: 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 computed
Severity69% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
30%
KEV
Not listed

Published

August 19, 2026

Last Modified

September 9, 2026

Advisory Details (3)

Auto-updated Aug 25, 2026
🔬 Proof of concept available. Patch available. Sources: github_commit, github_release, github.
github_release Patch Available

v0.7.1

Patch available: modelcontextprotocol/php-sdk v0.7.1

https://github.com/modelcontextprotocol/php-sdk/releases/tag/v0.7.1
github_commit Patch Available

commit 055593f2592e (modelcontextprotocol/php-sdk)

Patch available: modelcontextprotocol/php-sdk v0.7.1 (contains commit 055593f2592e)

https://github.com/modelcontextprotocol/php-sdk/commit/055593f2592e1d7f5f48587c999ca7068a3be90d
github Patch Available🟡 PoC Available

DoS: client HttpTransport SSE buffer (sseBuffer .= chunk) grows unbounded when server withholds the event delimiter · Advisory · modelcontextprotocol/php-sdk · GitHub

https://github.com/modelcontextprotocol/php-sdk/security/advisories/GHSA-7m52-jw36-44r3

Vendor Advisories for CVE-2026-53965(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)
Packagist(1)
PackageVulnerable rangeFixed inDependents
mcp/sdkv0.5.0, v0.6.0, v0.7.00.7.1—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 11× in last 7d / 46× 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.

  1. 2026-09-20 20:56 UTCEG score recompute
  2. 2026-09-20 20:16 UTCEPSS rescore
  3. 2026-09-19 21:20 UTCEG score recompute
  4. 2026-09-18 21:43 UTCEG score recompute
  5. 2026-09-18 19:28 UTCEPSS rescore
  6. 2026-09-17 21:29 UTCEG score recompute
  7. 2026-09-17 19:31 UTCEPSS rescore
  8. 2026-09-16 20:05 UTCEG score recompute
  9. 2026-09-16 14:08 UTCEPSS rescore
  10. 2026-09-16 05:15 UTCEPSS rescore
  11. 2026-09-15 19:17 UTCEG score recompute
  12. 2026-09-13 20:03 UTCEG score recompute
  13. 2026-09-13 16:47 UTCEPSS rescore
  14. 2026-09-12 20:26 UTCEG score recompute
  15. 2026-09-11 20:50 UTCEG score recompute
  16. 2026-09-11 14:53 UTCEPSS rescore
  17. 2026-09-10 21:01 UTCEG score recompute
  18. 2026-09-10 09:35 UTCEPSS rescore
  19. 2026-09-09 02:33 UTCEG score recompute
  20. 2026-09-08 22:01 UTCEPSS rescore
  21. 2026-09-07 20:04 UTCEG score recompute
  22. 2026-09-07 16:01 UTCEPSS rescore
  23. 2026-09-06 20:27 UTCEG score recompute
  24. 2026-09-06 13:47 UTCEPSS rescore
  25. 2026-09-05 20:50 UTCEG score recompute
Show 22 more
  1. 2026-09-04 21:14 UTCEG score recompute
  2. 2026-09-04 05:06 UTCEPSS rescore
  3. 2026-09-02 21:17 UTCEG score recompute
  4. 2026-09-02 14:12 UTCEPSS rescore
  5. 2026-09-01 19:56 UTCEG score recompute
  6. 2026-09-01 13:54 UTCEPSS rescore
  7. 2026-09-01 04:40 UTCEPSS rescore
  8. 2026-08-31 19:46 UTCEG score recompute
  9. 2026-08-30 19:17 UTCEPSS rescore
  10. 2026-08-30 19:01 UTCEG score recompute
  11. 2026-08-30 01:22 UTCEPSS rescore
  12. 2026-08-29 19:25 UTCEG score recompute
  13. 2026-08-28 21:41 UTCEPSS rescore
  14. 2026-08-27 15:59 UTCEG score recompute
  15. 2026-08-27 14:25 UTCEPSS rescore
  16. 2026-08-26 16:21 UTCEG score recompute
  17. 2026-08-26 16:00 UTCEG score recompute
  18. 2026-08-26 14:46 UTCEPSS rescore
  19. 2026-08-25 21:36 UTCEG score recompute
  20. 2026-08-25 20:55 UTCEG score recompute▲ 6.90
  21. 2026-08-25 20:54 UTCMITRE cvelistV5CVSS v3 → 6.9 · CVSS v4 → 6.9 · severity → MEDIUM
  22. 2026-08-19 19:42 UTCEG score recompute

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-53965?
CVE-2026-53965 is a medium vulnerability published on August 19, 2026. The MCP PHP SDK (Composer package mcp/sdk) is the official Model Context Protocol SDK for PHP. In versions 0.5.0 through 0.7.0, the HTTP client transport reads a Server-Sent Events response stream incrementally and appends each chunk to an in-memory buffer with no upper bound. The buffer is only…
When was CVE-2026-53965 disclosed?
CVE-2026-53965 was first published in the National Vulnerability Database on August 19, 2026, with the most recent update on September 9, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-53965 actively exploited?
CVE-2026-53965 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 70.4% of all scored CVEs.
What is the CVSS score of CVE-2026-53965?
CVE-2026-53965 has a CVSS v3 base score of 6.9 (NVD).
How do I remediate CVE-2026-53965?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-53965, 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

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