# 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.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Feb 2026
- **Updated:** 25 May 2026
- **Also known as:** GHSA-5wr5-vxhh-x7gm

## 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 (Deserialization of Untrusted Data)

## 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.

## 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:

- https://github.com/mbanyamer/CVE-2026-26221-Hyland-OnBase-Timer-Service-Unauthenticated-RCE (github_poc): https://github.com/mbanyamer/CVE-2026-26221-Hyland-OnBase-Timer-Service-Unauthenticated-RCE

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-26221 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-26221 in the wild and no public exploit code.

Affected product: Hyland OnBase Workflow Timer Service. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-26221/ (Markdown: https://insights.sbomify.com/CVE-2026-26221/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-26221
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-26221
- OSV: https://osv.dev/vulnerability/CVE-2026-26221

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-26221/
Summaries are generated and may contain mistakes; the official description above is the record.