CVE-2021-26556Public exploit

Local privilege escalation via writable DLL search path

Published Oct 7, 2021 · Updated Aug 3, 2024

Local privilege escalation in affected Windows releases of Octopus Server allows local users to execute code as Local System. A custom installation directory inherits a BUILTIN\Users ACL that lets unprivileged users add a poisoned CRYPTBASE.dll, which the Local System service loads. Exploitation requires a Windows custom-path installation and a service restart or reboot, after which attacker code runs with Local System privileges.

CVSS severity7.8
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Local privilege escalation in affected Windows releases of Octopus Server allows local users to execute code as Local System. A custom installation directory inherits a BUILTIN\Users ACL that lets unprivileged users add a poisoned CRYPTBASE.dll, which the Local System service loads. Exploitation requires a Windows custom-path installation and a service restart or reboot, after which attacker code runs with Local System privileges.

The record

CVE
CVE-2021-26556
Published
Oct 7, 2021
Updated
Aug 3, 2024
Vendor
Octopus Deploy
Product
Octopus Server
Classifications
CWE-426, T1574.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=0.9 <unspecified
  2. Affected versionversion=2020.5.0 <unspecified
  3. Affected versionversion=unspecified <2020.4.229
  4. Affected versionversion=unspecified <2020.5.256

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Octopus Deploy · Octopus Serverversion=0.9 <unspecified; version=2020.5.0 <unspecified; version=unspecified <2020.4.229; version=unspecified <2020.5.256

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
4.4NIST NVDAV:L/AC:M/Au:N/C:P/I:P/A:P

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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-426Untrusted Search Path
T1574.002DLL Side-Loading

Public exploit references

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

Technologies

Your stack

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Your stack

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