CVE-2021-26556

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-10-07 · updated 2026-06-17
Weakness: CWE-426

Description

When Octopus Server is installed using a custom folder location, folder ACLs are not set correctly and could lead to an unprivileged user using DLL side-loading to gain privileged access.

Affected products

Octopus Deploy: from 0.9 before 2020.4.229 — fixed in 2020.4.229
Octopus Deploy Octopus Server: from 2020.5.0 before 2020.5.256 — fixed in 2020.5.256

How to fix

Upgrade to a fixed version: Octopus Deploy 2020.4.229; Octopus Deploy Octopus Server 2020.5.256. Check the vendor advisory for mitigations.

References

https://advisories.octopus.com/adv/2021-01---Local-privilege-escalation-in-Octopus-Server-%28CVE-2021-26556%29.1733296189.html
https://advisories.octopus.com/adv/2021-01---Local-privilege-escalation-in-Octopus-Server-%28CVE-2021-26556%29.1733296189.html

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