Description

Improper verification of cryptographic signature in Microsoft Teams allows an unauthorized attacker to perform spoofing over a network.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-08-07T00:16:36.833Z",
  "pubdate": "2026-08-07T00:16:36.833Z",
  "executiveSummary": "This vulnerability involves an improper verification of cryptographic signature within Microsoft Teams, presenting a significant security risk to organizational communications.\nThe flaw allows an unauthorized remote attacker to perform spoofing attacks over a network, compromising the integrity and authenticity of data or messages processed by the application.\nThe affected product is Microsoft Teams. The primary impact of this security deficiency is the potential for message tampering, sender impersonation, and erosion of trust in collaborative sessions.\nRisk implications include unauthorized actors injecting malicious content or deceptive communications while appearing as legitimate participants within the network boundary.\nAttacker capabilities require network adjacency or remote network access to intercept, modify, or forge traffic intended for or originated by the application.\nExploitation requirements necessitate that the target system processes improperly validated cryptographic signatures, enabling the attacker to bypass trust boundaries without requiring prior authentication or elevated privileges.",
  "technicalDetails": "The root cause of this vulnerability lies in the insufficient or flawed validation logic applied to cryptographic signatures within Microsoft Teams.\nCryptographic signatures are designed to guarantee the authenticity and integrity of data packets, payloads, or messages by verifying that they originate from a trusted source and have not been altered in transit.\nDue to improper verification routines, the vulnerable component fails to adequately check signature validity, certificate chains, or integrity hashes against expected cryptographic anchors.\nAn unauthorized attacker leverages this flaw by crafting malicious network traffic or spoofed payloads containing invalid or manipulated signatures that the application incorrectly accepts as legitimate.\nThe attack flow proceeds as follows: First, the attacker positions themselves on the network or interacts with the target over the network protocol utilized by Microsoft Teams.\nSecond, the attacker transmits the spoofed data packet or message payload containing the bypassed cryptographic validation parameters.\nThird, the vulnerable cryptographic verification routine processes the incoming payload and, due to the lack of strict validation checks, incorrectly marks the signature as verified.\nFourth, the application proceeds to process the forged data as authentic, resulting in successful spoofing and potential downstream execution of unauthorized instructions or display of malicious content.\nAuthentication requirements are absent, as the vulnerability can be targeted by an unauthorized actor over the network.\nPrivilege requirements are minimal, requiring no pre-existing administrative or user-level access to the local system.\nNetwork exposure is present, as the attack vectors operate remotely across the network layer where Microsoft Teams communicates.\nPost-exploitation impact includes the ability to mislead users regarding message origin, facilitate social engineering attacks through trusted channels, and potentially compromise session integrity."
}