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Microsoft EUVD-2026-18532

| CVE-2026-34838 CRITICAL
Deserialization of Untrusted Data (CWE-502)
2026-04-02 GitHub_M
Microsoft Deserialization RCE
9.9
CVSS 3.1 · GitHub Advisory
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Severity by source

GitHub Advisory PRIMARY
9.9 CRITICAL
AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

6
Analysis Updated
Apr 16, 2026 - 05:46 EUVD-patch-fix
executive_summary
Re-analysis Queued
Apr 16, 2026 - 05:29 backfill_euvd_patch
patch_released
Patch available
Apr 16, 2026 - 05:29 EUVD
6.8.156,26.0.12,25.0.90
EUVD ID Assigned
Apr 02, 2026 - 19:31 euvd
EUVD-2026-18532
Analysis Generated
Apr 02, 2026 - 19:31 vuln.today
CVE Published
Apr 02, 2026 - 19:15 nvd
CRITICAL 9.9

DescriptionGitHub Advisory

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.

AnalysisAI

Remote Code Execution in Group-Office enterprise CRM via insecure deserialization allows authenticated attackers to write arbitrary files and execute code on the server. Affects all versions prior to 6.8.156, 25.0.90, and 26.0.12 across multiple product branches. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Authenticate to Group-Office instance
Delivery
Inject serialized FileCookieJar into settings string
Exploit
Trigger AbstractSettingsCollection deserialization
Execution
Write arbitrary file to server
Impact
Execute remote code
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Vulnerability AssessmentAI

Exploitation Authenticated user account on Group-Office versions prior to 6.8.156, 25.0.90, or 26.0.12 with access to settings modification functionality. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment This vulnerability presents critical real-world risk despite requiring authentication. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker with valid low-privileged credentials (such as a standard user account or compromised employee access) authenticates to an internet-accessible Group-Office instance. They navigate to a settings panel or use the application's API to modify a configuration value, injecting a serialized FileCookieJar object crafted to write a malicious PHP webshell to the server's web root directory (for example, /var/www/html/shell.php). …
Remediation Vendor-released patches are available across all affected version branches. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Inventory all Group-Office CRM deployments and document current versions. …

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EUVD-2026-18532 vulnerability details – vuln.today
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