CVE-2026-34838
Published: 02 April 2026
Summary
CVE-2026-34838 is a critical-severity Deserialization of Untrusted Data (CWE-502) vulnerability in Intermesh Group-Office. Its CVSS base score is 9.9 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 40.9% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-34838 is a critical insecure deserialization vulnerability (CWE-502, CVSS 9.9) affecting Group-Office, an enterprise customer relationship management and groupware tool. Versions prior to 6.8.156, 25.0.90, and 26.0.12 are vulnerable due to a flaw in the AbstractSettingsCollection model, which insecurely deserializes settings loaded from strings. Attackers can exploit this by injecting a serialized FileCookieJar object into a setting string.
An authenticated attacker with low privileges (PR:L) can exploit the vulnerability remotely (AV:N) with low attack complexity (AC:L) and no user interaction (UI:N), achieving a scope change (S:C) with high confidentiality, integrity, and availability impact (C:H/I:H/A:H). Successful exploitation enables arbitrary file write on the server, directly resulting in remote code execution (RCE).
The vulnerability is patched in Group-Office versions 6.8.156, 25.0.90, and 26.0.12. Security practitioners should upgrade immediately and review the official security advisory at https://github.com/Intermesh/groupoffice/security/advisories/GHSA-h22j-frrf-5vxq along with release notes at https://github.com/Intermesh/groupoffice/releases/tag/v6.8.156, https://github.com/Intermesh/groupoffice/releases/tag/v25.0.90, and https://github.com/Intermesh/groupoffice/releases/tag/v26.0.12 for mitigation details.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-18532
Vulnerability details
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Insecure deserialization in Group-Office web application enables remote exploitation of a public-facing application for arbitrary file write and RCE.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly mitigates the insecure deserialization vulnerability by requiring timely remediation through vendor patches in versions 6.8.156, 25.0.90, and 26.0.12.
Prevents exploitation by validating and sanitizing setting strings to block injection of malicious serialized objects like FileCookieJar before deserialization.
Detects unauthorized file writes and integrity violations resulting from successful deserialization exploits leading to RCE.