Threat Advisory

TLS 1.2 and DTLS Client Vulnerability Enables Unverified Cipher Acceptance

Threat: Vulnerability
Targeted Region: Global
Targeted Sector: Technology & IT
Criticality: Critical
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EXECUTIVE SUMMARY:

CVE-2026-55953 with a CVSS score of 9.1 is a vulnerability affecting TLS 1.2 and DTLS clients that facilitates a dangerous algorithm downgrade during the negotiation phase. This technical flaw arises because the client improperly accepts an anonymous cipher suite that the server never actually offered, which directly undermines the integrity of the server authentication process. An attacker can exploit this condition by inserting themselves into the communication path as a man-in-the-middle, manipulating the handshake to force the weaker encryption standard without needing internal network access. Once successful, the attacker gains the capability to completely bypass authentication verification, allowing them to intercept, read, or modify sensitive data in transit. The business impact of such a breach is significant, potentially resulting in the exposure of confidential corporate information and severe compliance violations. Successful exploitation specifically requires the targeted client to be actively negotiating a connection using TLS 1.2 or DTLS protocols with an external service.

RECOMMENDATIONS:

  • We recommend you to update TLS 1.2 and DTLS client to below version:
  • https://msrc.microsoft.com/update-guide/en-US/advisory/CVE-2026-55953

REFERENCES:

The following reports contain further technical details:[/subscribe_to_unlock_form]

EXECUTIVE SUMMARY:

CVE-2026-55953 with a CVSS score of 9.1 is a vulnerability affecting TLS 1.2 and DTLS clients that facilitates a dangerous algorithm downgrade during the negotiation phase. This technical flaw arises because the client improperly accepts an anonymous cipher suite that the server never actually offered, which directly undermines the integrity of the server authentication process. An attacker can exploit this condition by inserting themselves into the communication path as a man-in-the-middle, manipulating the handshake to force the weaker encryption standard without needing internal network access. Once successful, the attacker gains the capability to completely bypass authentication verification, allowing them to intercept, read, or modify sensitive data in transit. The business impact of such a breach is significant, potentially resulting in the exposure of confidential corporate information and severe compliance violations. Successful exploitation specifically requires the targeted client to be actively negotiating a connection using TLS 1.2 or DTLS protocols with an external service.

RECOMMENDATIONS:

  • We recommend you to update TLS 1.2 and DTLS client to below version:
  • https://msrc.microsoft.com/update-guide/en-US/advisory/CVE-2026-55953

REFERENCES:

The following reports contain further technical details:[emaillocker id="1283"]

[/emaillocker]
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