CVE-2021-26565Public exploitNetwork attack vector

Credential disclosure via QuickConnect HTTP downgrade

Published Feb 26, 2021 · Updated Sep 17, 2024

Cleartext transmission in synorelayd in Synology DiskStation Manager before 6.2.3-25426-3 allows man-in-the-middle attackers to steal credentials. QuickConnect redirects even HTTPS requests to an HTTP endpoint, allowing session traffic and cookies to traverse an unencrypted connection. QuickConnect must be enabled and a user must follow the service link; interception exposes device credentials without granting direct data modification.

CVSS severity8.3
High
EPSS probability0.73%
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

Cleartext transmission in synorelayd in Synology DiskStation Manager before 6.2.3-25426-3 allows man-in-the-middle attackers to steal credentials. QuickConnect redirects even HTTPS requests to an HTTP endpoint, allowing session traffic and cookies to traverse an unencrypted connection. QuickConnect must be enabled and a user must follow the service link; interception exposes device credentials without granting direct data modification.

The record

CVE
CVE-2021-26565
Published
Feb 26, 2021
Updated
Sep 17, 2024
Vendor
Synology
Product
Synology DiskStation Manager
Classifications
CWE-319, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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=unspecified <6.2.3-25426-3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Synology · Synology DiskStation Managerversion=unspecified <6.2.3-25426-3

Published CVSS scores

5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:P/I:N/A:N
8.3Synology Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-319Cleartext Transmission of Sensitive Information
T1557Adversary-in-the-Middle

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