CVE-2025-27136

CVE-2025-27136 is a medium-severity vulnerability with a CVSS 4.0 base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-611.

Key facts

Description

LocalS3 is an Amazon S3 mock service for testing and local development. Prior to version 1.21, the LocalS3 service's bucket creation endpoint is vulnerable to XML External Entity (XXE) injection. When processing the CreateBucketConfiguration XML document during bucket creation, the service's XML parser is configured to resolve external entities. This allows an attacker to declare an external entity that references an internal URL, which the server will then attempt to fetch when parsing the XML. The vulnerability specifically occurs in the location constraint processing, where the XML parser resolves external entities without proper validation or restrictions. When the external entity is resolved, the server makes an HTTP request to the specified URL and includes the response content in the parsed XML document. This vulnerability can be exploited to perform server-side request forgery (SSRF) attacks, allowing an attacker to make requests to internal services or resources that should not be accessible from external networks. The server will include the responses from these internal requests in the resulting bucket configuration, effectively leaking sensitive information. The attacker only needs to be able to send HTTP requests to the LocalS3 service to exploit this vulnerability.

Frequently asked questions

What is CVE-2025-27136?
LocalS3 is an Amazon S3 mock service for testing and local development. Prior to version 1.21, the LocalS3 service's bucket creation endpoint is vulnerable to XML External Entity (XXE) injection. When processing the CreateBucketConfiguration XML document during bucket creation, the service's XML parser is configured to resolve external entities. This allows an attacker to declare an external entity that references an internal URL, which the server will then attempt to fetch when parsing the XML. The vulnerability specifically occurs in the location constraint processing, where the XML parser resolves external entities without proper validation or restrictions. When the external entity is resolved, the server makes an HTTP request to the specified URL and includes the response content in the parsed XML document. This vulnerability can be exploited to perform server-side request forgery (SSRF) attacks, allowing an attacker to make requests to internal services or resources that should not be accessible from external networks. The server will include the responses from these internal requests in the resulting bucket configuration, effectively leaking sensitive information. The attacker only needs to be able to send HTTP requests to the LocalS3 service to exploit this vulnerability.
How severe is CVE-2025-27136?
CVE-2025-27136 has a CVSS 4.0 base score of 5.5, rated medium severity.
Is CVE-2025-27136 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (39th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2025-27136?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2025-27136 have an EU (EUVD) identifier?
Yes. CVE-2025-27136 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-7729.
When was CVE-2025-27136 published?
CVE-2025-27136 was published on 2025-03-10 and last updated on 2026-06-17.

References

Other CWE-611 (Improper Restriction of XML External Entity Reference (XXE)) vulnerabilities

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