CVE-2026-4270

Q: How do I fix CVE-2026-4270?

Upgrade aws api mcp server to 1.3.9 or later.

Q: Is CVE-2026-4270 being actively exploited?

Not that we know of. CVE-2026-4270 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.13% is the estimated probability that it will be exploited in the next 30 days. That is higher than 3% of all scored CVEs.

Q: How severe is CVE-2026-4270?

CVE-2026-4270 has a CVSS v3 base score of 5.5, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2026-4270 affect?

Published advisories record a fix for aws api mcp server (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

MEDIUM

5.5

CVSS v3

NVD

Description

Improper Protection of Alternate Path exists in the no-access and workdir feature of the AWS API MCP Server versions >= 0.2.14 and < 1.3.9 on all platforms may allow the bypass of intended file access restriction and expose arbitrary local file contents in the MCP client application context. To remediate this issue, users should upgrade to version 1.3.9.

CWE-424

How to fix

Remediation Available

aws api mcp serverNVD

Affected:>= 0.2.14, < 1.3.9Fixed in:1.3.9CVE-2026-4270derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorLocal

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityNone

AvailabilityNone

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Exploit Intelligence

0.13%probability of exploitation in 30 days

3rdpercentile

Low risk: more likely to be exploited than 3% of all known CVEs.

References

Vendor Advisory1

aws.amazon.com

Third-Party Advisory1

pypi.org

Related Vulnerabilities

Other CWE-424 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-58136	Critical	9.0	85%	KEV	Fix
CVE-2025-48827	Critical	10.0	77%	-	-
CVE-2025-48828	Critical	9.0	60%	-	-
CVE-2019-18997	Medium	4.3	1.5%	-	-
CVE-2023-20272	Medium	6.7	0.9%	-	-
CVE-2021-3793	Medium	6.5	0.7%	-	Fix

Common questions

How do I fix CVE-2026-4270?

Upgrade aws api mcp server to 1.3.9 or later.

Is CVE-2026-4270 being actively exploited?

Not that we know of. CVE-2026-4270 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.13% is the estimated probability that it will be exploited in the next 30 days. That is higher than 3% of all scored CVEs.

How severe is CVE-2026-4270?

CVE-2026-4270 has a CVSS v3 base score of 5.5, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-4270 affect?

Published advisories record a fix for aws api mcp server (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-21.