CVE-2026-9739

CRITICALNVD 9.49.4
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

This critical-severity CVE scores 9.4 under NVD CVSS v3. EPSS exploit probability: 0.3% (20th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, NVD CVSS v3
Trending — 3 sources updated this week

Also known asEUVD-2026-32672 (ENISA EUVD) · GHSA-7pf3-8xx7-rvhf (GitHub Security Advisories)Source: ENISA EUVD

9.4EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 9.4Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented allowed-origins and allowed-hosts flags to align with MCP security guidelines. However, the hardcoded Access-Control-Allow-Origin: * header in the SSE initialization handler was inadvertently retained. This vulnerability specifically impacts users connecting via Toolbox using SSE under specification v2024-11-05.

CVSS v3
9.4
EG Score
9.4CRITICALmedium confidence
EG Risk
42
EG Risk 42/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity94% × 45%
Impact severity (EG Severity): CVSS 9.4 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.3% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
20th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (9.4): severity, escalated by confirmed exploitation. This CVE's 9.4 is its impact severity (EG Severity), not escalated.

EG Severity
9.4 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-02). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

May 27, 2026

Last Modified

October 26, 2026

Advisory Details (2)

Auto-updated Oct 2, 2026
Patch available. Sources: github_pr.
GitHub pull request Patch Available

fix: remove hardcoded * allowed origin for sse

Patch available: googleapis/mcp-toolbox v1.2.0 (PR #3054 merged 2026-04-16)

https://github.com/googleapis/mcp-toolbox/pull/3054
Web page

[SECURITY] Hardcoded CORS bypass on SSE endpoint in internal/server/mcp.go · Issue #3053 · googleapis/mcp-toolbox · GitHub

https://github.com/googleapis/mcp-toolbox/issues/3053

Vendor Advisories for CVE-2026-9739(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
gogithub.com/googleapis/mcp-toolbox @ 1.2.0 (fixes < 1.2.0)—ghsa

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
Go(1)
PackageVulnerable rangeFix by version rangeDependents
github.com/googleapis/mcp-toolbox—
  • every version up to 1.2.0: fixed in 1.2.0
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 15× in last 7d / 57× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 329 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 229 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-02 22:51 UTCEG score recompute
  2. 2026-11-02 22:51 UTCGHSA enrichmentGHSA-7pf3-8xx7-rvhf · GitHub severity CRITICAL
  3. 2026-11-02 16:46 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  4. 2026-11-01 21:16 UTCEG score recompute
  5. 2026-11-01 21:16 UTCGHSA enrichmentGHSA-7pf3-8xx7-rvhf · GitHub severity CRITICAL
  6. 2026-10-31 19:42 UTCEG score recompute
  7. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  8. 2026-10-30 18:08 UTCEG score recompute
  9. 2026-10-30 16:35 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  10. 2026-10-29 16:34 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  11. 2026-10-29 16:33 UTCEG score recompute
  12. 2026-10-28 16:33 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  13. 2026-10-28 14:59 UTCEG score recompute
  14. 2026-10-27 16:33 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  15. 2026-10-27 13:16 UTCEG score recompute
  16. 2026-10-26 16:33 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  17. 2026-10-26 09:07 UTCEG score recompute
  18. 2026-10-25 16:34 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  19. 2026-10-25 13:48 UTCEG score recompute
  20. 2026-10-25 07:31 UTCEG score recompute
  21. 2026-10-24 16:34 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  22. 2026-10-24 05:56 UTCEG score recompute
  23. 2026-10-23 16:33 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  24. 2026-10-23 04:21 UTCEG score recompute
  25. 2026-10-22 16:35 UTCEPSS rescoreEPSS 0.2% · 13th percentile
Show 75 more
  1. 2026-10-22 02:47 UTCEG score recompute
  2. 2026-10-21 16:34 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  3. 2026-10-21 01:11 UTCEG score recompute
  4. 2026-10-20 16:34 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  5. 2026-10-19 23:37 UTCEG score recompute
  6. 2026-10-19 16:34 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  7. 2026-10-18 22:01 UTCEG score recompute
  8. 2026-10-18 16:33 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  9. 2026-10-18 02:56 UTCEG score recompute
  10. 2026-10-17 19:58 UTCEG score recompute
  11. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  12. 2026-10-16 18:23 UTCEG score recompute
  13. 2026-10-16 16:45 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  14. 2026-10-15 16:33 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  15. 2026-10-15 14:47 UTCEG score recompute
  16. 2026-10-14 16:34 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  17. 2026-10-14 09:19 UTCEG score recompute
  18. 2026-10-13 16:35 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  19. 2026-10-13 06:40 UTCEG score recompute
  20. 2026-10-12 16:35 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  21. 2026-10-12 14:40 UTCEG score recompute
  22. 2026-10-11 19:11 UTCEG score recompute
  23. 2026-10-11 16:26 UTCEG score recompute
  24. 2026-10-11 13:50 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  25. 2026-10-11 13:38 UTCEG score recompute
  26. 2026-10-10 20:01 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  27. 2026-10-09 20:08 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  28. 2026-10-08 17:14 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  29. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  30. 2026-10-06 15:19 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  31. 2026-10-05 17:44 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  32. 2026-10-04 23:23 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  33. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  34. 2026-10-02 17:57 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  35. 2026-10-01 19:51 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  36. 2026-09-30 15:04 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  37. 2026-09-29 15:24 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  38. 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  39. 2026-09-27 13:49 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  40. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  41. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  42. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  43. 2026-09-22 16:01 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  44. 2026-09-21 21:09 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  45. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  46. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  47. 2026-09-17 19:32 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  48. 2026-09-16 14:09 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  49. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  50. 2026-09-15 03:12 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  51. 2026-09-14 07:32 UTCEG score recompute
  52. 2026-09-13 16:48 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  53. 2026-09-12 15:02 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  54. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  55. 2026-09-11 09:38 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  56. 2026-09-10 09:35 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  57. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  58. 2026-09-06 13:48 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  59. 2026-09-05 15:31 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  60. 2026-09-04 05:07 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  61. 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  62. 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  63. 2026-09-01 04:40 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  64. 2026-08-30 19:18 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  65. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  66. 2026-08-28 21:42 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  67. 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  68. 2026-08-26 14:47 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  69. 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  70. 2026-08-25 05:09 UTCEG score recompute
  71. 2026-08-24 14:18 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  72. 2026-08-23 14:52 UTCEG score recompute
  73. 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  74. 2026-08-22 00:41 UTCEG score recompute
  75. 2026-08-21 23:49 UTCEPSS rescoreEPSS 0.3% · 20th percentile

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-9739?
CVE-2026-9739 is a critical-severity vulnerability; its CVE record was published on May 27, 2026. Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented allowed-origins and allowed-hosts flags to align with MCP security guidelines. However, the hardcoded Access-Control-Allow-Origin: * header in the SSE initialization handler was…
When was the CVE record for CVE-2026-9739 published?
The CVE record for CVE-2026-9739 was published on May 27, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of October 26, 2026; the record at its source may have been updated since.
Is CVE-2026-9739 actively exploited?
CVE-2026-9739 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (20th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-9739?
CVE-2026-9739 has a CVSS v3 base score of 9.4 (NVD).
How do I remediate CVE-2026-9739?
A fix for CVE-2026-9739 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-9739 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-9739

Explore →

Is Your Infrastructure Affected by CVE-2026-9739?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Book a Demo →Browse All CVEs