Description

Deserialization of untrusted data in Microsoft Entra ID allows an unauthorized attacker to execute code over a network.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "10.0",
  "pubDate": "2026-08-20T22:18:00.740Z",
  "pubdate": "2026-08-20T22:18:00.740Z",
  "executiveSummary": "A deserialization of untrusted data vulnerability has been identified within Microsoft Entra ID. This security flaw enables an unauthorized remote threat actor to execute arbitrary code over the network without requiring user interaction or prior authentication.\nThe vulnerability resides in the core handling of serialized objects, where incoming data streams are improperly validated before being processed by the application runtime. If an attacker crafts a malicious payload containing specially formatted serialized objects, the vulnerable component will deserialize the input, inadvertently triggering the execution of embedded instructions.\nThe business impact of this vulnerability is critical, potentially leading to total system compromise, unauthorized access to sensitive directory services, and lateral movement within the enterprise cloud infrastructure.\nExploitation requirements are limited to network connectivity to the vulnerable Microsoft Entra ID endpoint capable of processing the malicious serialization payload. Given the remote exploitability and lack of authentication prerequisites, immediate remediation and monitoring are strongly advised to prevent active exploitation.",
  "technicalDetails": "The root cause of the vulnerability stems from insecure deserialization practices within the data processing routines of Microsoft Entra ID. Applications that ingest serialized objects without implementing robust cryptographic integrity checks or strict type-whitelisting are inherently susceptible to object injection attacks.\nThe vulnerable component is responsible for parsing and instantiating objects passed via network protocols from untrusted sources. When the component processes a maliciously crafted payload, it blindly reconstructs the object graph specified by the attacker. During the deserialization lifecycle, particularly if classes implement dangerous gadget chains (such as custom readObject methods or callbacks), the execution flow can be hijacked.\nThe attack flow proceeds as follows: First, the unauthorized attacker identifies the network-exposed endpoint accepting serialized data structures. Second, the attacker crafts a tailored exploit payload containing serialized objects designed to invoke specific system APIs or execute arbitrary binaries upon instantiation. Third, the attacker transmits this payload over the network to the targeted Microsoft Entra ID service.\nUpon receipt, the vulnerable component attempts to deserialize the data stream. Because input validation is absent or insufficient, the malicious gadget chain is triggered within the application memory space. This results in arbitrary code execution with the privileges of the underlying service account.\nAuthentication and privilege requirements for this exploit are minimal; the vulnerability allows an unauthorized attacker to achieve execution remotely over a network. The post-exploitation impact includes complete compromise of the affected service node, potential data exfiltration of directory contents, and the establishment of persistent access within the affected environment."
}