Mbed TLS TLS 1.3 Session Ticket RNG Logic Flaw Leading to Data Integrity Issues (CVE-2026-73064)

CVE-2026-73064: Random Number Generator Failure Can Compromise TLS Data Integrity Vulnerability Overview Vulnerability Type: Logic Error Description: The function incorrectly returns instead of a negative error code when the random number generator ( ) fails. Attack Scenario: An attacker who can disrupt the entropy source (e.g., via physical or local access) to cause random number generation failure may exploit this flaw. Potential Impact: - If the application calls before the handshake is complete, an attacker can inject additional data (controlling the number of injected bytes, but not their content). - If the application calls after the handshake is complete, an attacker can cause some initial bytes to not be sent by the server. Severity: Low (LOW) Impact: TLS 1.3 application data integrity Affected Versions Affected Versions: - Mbed TLS 3.x: 3.2.0 through 3.6.6 - Mbed TLS 4.0.0 and 4.1.0 Unaffected Versions: - Mbed TLS 3.6.7 and later - Mbed TLS 4.1.1 and later - Mbed TLS 4.2.0 and later Specific Conditions: - Affects only TLS 1.3 servers (TLS 1.2 is not affected). - Affects only when the application calls or before the initial TLS handshake is complete. - Affects only when is enabled and a ticket callback function is configured. - By default, the random number generator is configured to fail if the entropy source fails; this can be avoided by setting the reseed interval to . Remediation Upgrade Recommendation: - Affected users should upgrade to Mbed TLS 3.6.7, Mbed TLS 4.1.1, or Mbed TLS 4.2.0 (depending on the branch being tracked). Work-around: - Ensure the application does not call or before the initial TLS handshake is complete. - Disable TLS 1.3 session tickets (by disabling or setting the ticket callback function to ). - Set the random number generator's reseed interval to to avoid triggering the issue when the entropy source fails. Fix Commits > Note: POC code or exploitation code is not included on this page.

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Mbed TLS TLS 1.3 Session Ticket RNG Logic Flaw Leading to Data Integrity Issues (CVE-2026-73064)