🟠 High | Source: Microsoft Security Response Center
CVE-2026-54891 is a TLS vulnerability in which plaintext APPLICATION_DATA is injected during the TLS handshake and subsequently delivered to the client application after the handshake completes. This means data intended to be protected by encryption may be processed by the application before a secure channel is fully established, potentially exposing sensitive information or enabling data manipulation. The flaw is particularly concerning in cloud environments where TLS is the primary transport security mechanism.
Security Architect’s Take: Audit any Azure-hosted services or workloads relying on the affected SSL/TLS library and apply available patches immediately; additionally, review network telemetry for anomalous plaintext data appearing during or just after TLS handshake phases as a potential indicator of exploitation.
Original advisory: CVE-2026-54891 Plaintext APPLICATION_DATA injected during TLS handshake delivered to client application post-handshake in ssl