CVE-2020-8138Public exploitNetwork attack vector

Internal resource access via IPv4-mapped IPv6 URLs

Published Mar 20, 2020 · Updated Aug 4, 2024

Server-side request forgery in Nextcloud Server before 15.0.14, 16.0.7, and 17.0.2 allows remote authenticated users to access internal resources. The calendar subscription URL check fails to detect an IPv4 address embedded in an IPv6 literal, allowing the server-side fetcher to reach otherwise blocked destinations. A user account and the ability to subscribe to a crafted calendar URL are required; successful exploitation can expose data returned by intranet or loopback services.

CVSS severity6.3
Medium
EPSS probability1.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Server-side request forgery in Nextcloud Server before 15.0.14, 16.0.7, and 17.0.2 allows remote authenticated users to access internal resources. The calendar subscription URL check fails to detect an IPv4 address embedded in an IPv6 literal, allowing the server-side fetcher to reach otherwise blocked destinations. A user account and the ability to subscribe to a crafted calendar URL are required; successful exploitation can expose data returned by intranet or loopback services.

The record

CVE
CVE-2020-8138
Published
Mar 20, 2020
Updated
Aug 4, 2024
Vendor
Nextcloud GmbH
Product
Nextcloud Server
Classifications
CWE-918, T1090.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 20, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Fixed in 17.0.2, 16.0.7, and 15.0.14

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Nextcloud GmbH · Nextcloud Serverversion=Fixed in 17.0.2, 16.0.7, and 15.0.14

Published CVSS scores

6.5NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
6.3NextcloudCVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
4.0NVDAV:N/AC:L/Au:S/C:P/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1090.001Internal Proxy

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo