CVE-2021-39195Network attack vector

Internal data disclosure via unrestricted URL downloads

Published Sep 7, 2021 · Updated Aug 4, 2024

SSRF in Misskey before 12.90.0 allows remote authenticated users to read non-public internal-network data through server-side downloads. The downloadUrl function passed URLs from Upload from URL and remote attachment handling to its HTTP client without rejecting private resolved addresses. Reachability comes through authenticated URL upload or remote attachment processing; successful requests disclose internal data to the requester.

CVSS severity7.7
High
EPSS probability1.06%
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

SSRF in Misskey before 12.90.0 allows remote authenticated users to read non-public internal-network data through server-side downloads. The downloadUrl function passed URLs from Upload from URL and remote attachment handling to its HTTP client without rejecting private resolved addresses. Reachability comes through authenticated URL upload or remote attachment processing; successful requests disclose internal data to the requester.

The record

CVE
CVE-2021-39195
Published
Sep 7, 2021
Updated
Aug 4, 2024
Vendor
Misskey Project
Product
Misskey
Classifications
CWE-918, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 7, 2021CVE 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=< 12.90.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Misskey Project · Misskeyversion=< 12.90.0

Published CVSS scores

4.0NISTAV:N/AC:L/Au:S/C:P/I:N/A:N
6.5NISTCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
7.7GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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