CVE-2026-34838 Group-Office: Authenticated Remote Code Execution via PHP Insecure Deserialization in `AbstractSettingsCollection`

Critical 10.0 Published 2 Apr 2026 Updated 3 Apr 2026

An authenticated attacker can achieve remote code execution by injecting a serialized object into settings, allowing arbitrary file writes on the server.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-34838?

CVE-2026-34838 is a critical unsafe deserialization vulnerability in Intermesh groupoffice, published on 2 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Group-Office is an enterprise customer relationship management and groupware tool. Prior to versions 6.8.156, 25.0.90, and 26.0.12, a vulnerability in the AbstractSettingsCollection model leads to insecure deserialization when these settings are loaded. By injecting a serialized FileCookieJar object into a setting string, an authenticated attacker can achieve Arbitrary File Write, leading directly to Remote Code Execution (RCE) on the server. This issue has been patched in versions 6.8.156, 25.0.90, and 26.0.12.

Weakness: CWE-502

Which versions are affected by CVE-2026-34838?

It affects 1 product.

Products include Intermesh Group-Office.

How do I fix CVE-2026-34838?

No fix has been published for CVE-2026-34838 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-2026-34838 being exploited?

There is no known exploitation of CVE-2026-34838 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

Sources

Also known as GHSA-h22j-frrf-5vxq.