CVE-2026-49857

HIGHPre-NVD 7.47.4—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.4 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 72% 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
7.4EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 7.4Exploit: None knownExposed: 0

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

auth-fetch-mcp is an MCP server that lets AI assistants fetch content from authenticated web pages. Version 3.0.1 implements SSRF protection in assertSafeUrl() (src/security.ts) to block requests to private and loopback addresses. However, the isPrivateV6() function fails to detect IPv4-mapped IPv6 loopback addresses in their hex-normalized form. When an attacker supplies a URL such as http://[::ffff:127.0.0.1]:PORT/, the Node.js WHATWG URL parser silently normalizes the host to [::ffff:7f00:1]. Because net.isIPv4('7f00:1') returns false, the private-IP check is bypassed and the URL is passed to the browser or HTTP client, allowing the MCP tool to reach loopback services that are supposed to be blocked. The issue is exploitable under default configuration without any special environment variable. Version 3.0.1 patches the issue.

CVSS v3
7.4
EG Score
7.4(medium)
EG Risk
33(Track)
EG Risk 33/100SSVC: 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
Severity74% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
28%
KEV
Not listed

Published

July 1, 2026

Last Modified

August 13, 2026

Advisory Details (3)

Auto-updated Aug 13, 2026
🔬 Proof of concept available. Patch available. Sources: github, github_commit, github_release.
github_release Patch Available

v3.0.1

Patch available: ymw0407/auth-fetch-mcp v3.0.1

https://github.com/ymw0407/auth-fetch-mcp/releases/tag/v3.0.1
github_commit Patch Available

commit c5c523cd55b2 (ymw0407/auth-fetch-mcp)

Patch available: ymw0407/auth-fetch-mcp v3.0.1 (contains commit c5c523cd55b2)

https://github.com/ymw0407/auth-fetch-mcp/commit/c5c523cd55b24ae1680c5bacef95d59a81ae3450
github Patch Available🟡 PoC Available

SSRF Protection Bypass via IPv4-mapped IPv6 Loopback · Advisory · ymw0407/auth-fetch-mcp · GitHub

https://github.com/ymw0407/auth-fetch-mcp/security/advisories/GHSA-pvrj-8cg3-j5f8

Vendor Advisories for CVE-2026-49857(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)
npm(1)
PackageVulnerable rangeFixed inDependents
auth-fetch-mcp—3.0.2—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 7× in last 7d / 42× 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. 2026-09-11 14:53 UTCEPSS rescore
  2. 2026-09-10 09:35 UTCEPSS rescore
  3. 2026-09-08 22:01 UTCEPSS rescore
  4. 2026-09-07 16:01 UTCEPSS rescore
  5. 2026-09-06 14:27 UTCEG score recompute
  6. 2026-09-06 13:47 UTCEPSS rescore
  7. 2026-09-06 02:20 UTCEG score recompute
  8. 2026-09-04 05:06 UTCEPSS rescore
  9. 2026-09-02 14:12 UTCEPSS rescore
  10. 2026-09-01 13:54 UTCEPSS rescore
  11. 2026-09-01 04:40 UTCEPSS rescore
  12. 2026-08-30 22:40 UTCEG score recompute
  13. 2026-08-30 19:17 UTCEPSS rescore
  14. 2026-08-30 11:46 UTCEG score recompute
  15. 2026-08-30 01:22 UTCEPSS rescore
  16. 2026-08-28 21:41 UTCEPSS rescore
  17. 2026-08-27 22:26 UTCEG score recompute
  18. 2026-08-27 14:25 UTCEPSS rescore
  19. 2026-08-26 14:46 UTCEPSS rescore
  20. 2026-08-25 13:49 UTCEPSS rescore
  21. 2026-08-24 21:02 UTCEG score recompute
  22. 2026-08-23 06:52 UTCEG score recompute
  23. 2026-08-23 00:19 UTCEPSS rescore
  24. 2026-08-22 07:10 UTCEG score recompute
  25. 2026-08-21 23:49 UTCEPSS rescore
Show 21 more
  1. 2026-08-21 04:32 UTCEG score recompute
  2. 2026-08-20 22:55 UTCEPSS rescore
  3. 2026-08-20 04:41 UTCEG score recompute
  4. 2026-08-19 17:04 UTCEPSS rescore
  5. 2026-08-18 20:59 UTCEG score recompute
  6. 2026-08-18 13:48 UTCEPSS rescore
  7. 2026-08-17 23:26 UTCEG score recompute
  8. 2026-08-17 13:47 UTCEPSS rescore
  9. 2026-08-16 22:31 UTCEG score recompute
  10. 2026-08-16 14:56 UTCEPSS rescore
  11. 2026-08-16 11:37 UTCEG score recompute
  12. 2026-08-16 02:14 UTCEPSS rescore
  13. 2026-08-15 02:59 UTCEG score recompute
  14. 2026-08-15 01:30 UTCEPSS rescore
  15. 2026-08-13 18:19 UTCEG score recompute
  16. 2026-08-13 18:12 UTCEG score recompute
  17. 2026-08-13 15:28 UTCEG score recompute
  18. 2026-07-30 10:06 UTCEG score recompute
  19. 2026-07-26 13:16 UTCEG score recompute
  20. 2026-07-23 03:18 UTCEG score recompute
  21. 2026-07-01 19:05 UTCEG score recompute

Frequently asked(5)

What is CVE-2026-49857?
CVE-2026-49857 is a high vulnerability published on July 1, 2026. auth-fetch-mcp is an MCP server that lets AI assistants fetch content from authenticated web pages. Version 3.0.1 implements SSRF protection in assertSafeUrl() (src/security.ts) to block requests to private and loopback addresses. However, the isPrivateV6() function fails to detect IPv4-mapped IPv6…
When was CVE-2026-49857 disclosed?
CVE-2026-49857 was first published in the National Vulnerability Database on July 1, 2026, with the most recent update on August 13, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-49857 actively exploited?
CVE-2026-49857 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 72.2% of all scored CVEs.
What is the CVSS score of CVE-2026-49857?
CVE-2026-49857 has a CVSS v3 base score of 7.4 (NVD).
How do I remediate CVE-2026-49857?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-49857, 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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