CVE-2026-26221 Hyland OnBase Timer Service Unauthenticated .NET Remoting RCE
Unauthenticated .NET Remoting deserialization in Hyland OnBase allows remote attackers to achieve arbitrary file read/write and remote code execution.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-26221?
CVE-2026-26221 is a critical unsafe deserialization vulnerability in Hyland OnBase Workflow Timer Service, published on 13 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Hyland OnBase contains an unauthenticated .NET Remoting exposure in the OnBase Workflow Timer Service (Hyland.Core.Workflow.NTService.exe). An attacker who can reach the service can send crafted .NET Remoting requests to default HTTP channel endpoints on TCP/8900 (e.g., TimerServiceAPI.rem and TimerServiceEvents.rem for Workflow) to trigger unsafe object unmarshalling, enabling arbitrary file read/write. By writing attacker-controlled content into web-accessible locations or chaining with other OnBase features, this can lead to remote code execution. The same primitive can be abused by supplying a UNC path to coerce outbound NTLM authentication (SMB coercion) to an attacker-controlled host.
Weakness: CWE-502
Which versions are affected by CVE-2026-26221?
How do I fix CVE-2026-26221?
No fix has been published for CVE-2026-26221 yet. Limit exposure of the affected software until one is available.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2026-26221 being exploited?
There is no known exploitation of CVE-2026-26221 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as GHSA-5wr5-vxhh-x7gm.