CVE-2026-80347

HIGHPre-NVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 80% 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
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.5Exploit: Elevated riskExposed: 0

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

mcp-fetch checks a fetch target against its SSRF guard without removing the brackets that surround an IPv6 literal. isSafeUrl reads the hostname from the parsed URL, which for a literal such as http://[::1]/ yields the bracketed string, and then tests it with net.isIP. That call returns zero for a bracketed value, so the branch holding the private-address checks is skipped entirely. The guard falls back to resolving the hostname, the bracketed string is not a resolvable name, no addresses are returned, and the target is reported safe. The HTTP client then strips the brackets and connects. Because the address may be given in IPv4-mapped form, the same path reaches any IPv4 target the loopback and private checks were meant to exclude, including link-local metadata endpoints. isPrivateIPv6 also has no case for the ::ffff: prefix, so the mapped form would still pass even if the brackets were removed. The fetch target is supplied as a tool argument, so an attacker who can influence what the model requests can read internal responses back into the model context.

CVSS v3
7.5
EG Score
7.5(medium)
EG Risk
65(Attend)
EG Risk 65/100SSVC: Attend

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
Severity75% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
20%
KEV
Not listed

Published

August 26, 2026

Last Modified

August 26, 2026

Advisory Details (3)

Auto-updated Aug 26, 2026
No patch confirmed yet.
generic

mcp-fetch through 1.6.3 Server-Side Request Forgery via Unstripped IPv6 Literal Brackets | Advisories | VulnCheck

https://www.vulncheck.com/advisories/mcp-fetch-through-1.6.3-server-side-request-forgery-via-unstripped-ipv6-literal-brackets
generic

SSRF guard bypass via IPv6 literal (brackets not stripped before net.isIP) · Issue #16 · kazuph/mcp-fetch · GitHub

https://github.com/kazuph/mcp-fetch/issues/16
generic

GitHub - kazuph/mcp-fetch · GitHub

https://github.com/kazuph/mcp-fetch

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 12× in last 7d / 48× 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. 2026-09-21 05:31 UTCEG score recompute
  2. 2026-09-20 20:16 UTCEPSS rescore
  3. 2026-09-19 16:57 UTCEG score recompute
  4. 2026-09-19 04:43 UTCEG score recompute
  5. 2026-09-18 19:28 UTCEPSS rescore
  6. 2026-09-18 04:21 UTCEG score recompute
  7. 2026-09-16 15:46 UTCEG score recompute
  8. 2026-09-16 14:08 UTCEPSS rescore
  9. 2026-09-16 05:15 UTCEPSS rescore
  10. 2026-09-15 15:22 UTCEG score recompute
  11. 2026-09-15 03:12 UTCEPSS rescore
  12. 2026-09-15 03:12 UTCEPSS rescore
  13. 2026-09-14 02:47 UTCEG score recompute
  14. 2026-09-13 02:25 UTCEG score recompute
  15. 2026-09-12 02:03 UTCEG score recompute
  16. 2026-09-11 14:53 UTCEPSS rescore
  17. 2026-09-11 14:53 UTCEPSS rescore
  18. 2026-09-10 13:28 UTCEG score recompute
  19. 2026-09-09 00:52 UTCEG score recompute
  20. 2026-09-08 22:01 UTCEPSS rescore
  21. 2026-09-07 22:51 UTCEG score recompute
  22. 2026-09-06 22:26 UTCEG score recompute
  23. 2026-09-06 13:48 UTCEPSS rescore
  24. 2026-09-05 21:55 UTCEG score recompute
  25. 2026-09-05 15:31 UTCEPSS rescore
Show 23 more
  1. 2026-09-04 21:30 UTCEG score recompute
  2. 2026-09-04 09:14 UTCEG score recompute
  3. 2026-09-04 05:07 UTCEPSS rescore
  4. 2026-09-02 20:35 UTCEG score recompute
  5. 2026-09-02 14:12 UTCEPSS rescore
  6. 2026-09-01 19:10 UTCEG score recompute
  7. 2026-09-01 13:54 UTCEPSS rescore
  8. 2026-09-01 06:52 UTCEG score recompute
  9. 2026-09-01 04:40 UTCEPSS rescore
  10. 2026-09-01 04:40 UTCEPSS rescore
  11. 2026-08-31 06:09 UTCEG score recompute
  12. 2026-08-30 19:18 UTCEPSS rescore
  13. 2026-08-30 19:17 UTCEPSS rescore
  14. 2026-08-30 05:43 UTCEG score recompute
  15. 2026-08-30 01:22 UTCEPSS rescore
  16. 2026-08-29 05:17 UTCEG score recompute
  17. 2026-08-28 21:42 UTCEPSS rescore
  18. 2026-08-27 16:25 UTCEG score recompute
  19. 2026-08-27 14:25 UTCEPSS rescore
  20. 2026-08-26 15:54 UTCEG score recompute
  21. 2026-08-26 12:19 UTCEG score recompute
  22. 2026-08-26 10:18 UTCEG score recompute
  23. 2026-08-26 10:17 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-80347?
CVE-2026-80347 is a high vulnerability published on August 26, 2026. mcp-fetch checks a fetch target against its SSRF guard without removing the brackets that surround an IPv6 literal. isSafeUrl reads the hostname from the parsed URL, which for a literal such as http://[::1]/ yields the bracketed string, and then tests it with net.isIP. That call returns zero for a…
When was CVE-2026-80347 disclosed?
CVE-2026-80347 was first published in the National Vulnerability Database on August 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-80347 actively exploited?
CVE-2026-80347 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 79.7% of all scored CVEs.
What is the CVSS score of CVE-2026-80347?
CVE-2026-80347 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-80347?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-80347, 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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